Well, not really conversations. Lara hardly says anything to them, and you have no playable options to extend those few brief exchanges.
(Well, practically no. Turns out, if you intentionally prolong the fight on the Endurance's deck, or better yet, let Boris get a couple hits in, there's more dialog triggered. Lara will even yell, "Will you shut up!" at one point.)
In any case, I've been skulking around the island seeing how many extra Solarii I can trigger and, with luck, listen in on their conversations. What makes this happen is thus; the game provides a lot of collectibles. You can make it to the end game without bothering to pick up a single one (the only plot-important items are handed to you in cut scenes). But for whatever reason, the designers decided to implement a system that lets you keep the same saved game but go back to previously crossed areas to search for additional relics.
Because in the standard progression, your path is often broken behind you (forcing you to stay on the tracks of the railroad plot) the way the designers chose is by the somewhat reality-straining Instant Transport function. From any camp, you can immediately visit another camp.
To keep things interesting, when you do this re-visit, there are fresh mooks guarding the goodies. Like all the mooks, they appear to be triggered by you crossing certain points on the map. You can very much search a room thoroughly, then walk across the entrance and spawn a couple mooks in the middle of a long game of chess right where you were searching. And this sort of thing happens more often when you are on the less linear path of trying to collect every last mushroom or coin or whatever.
Because these encounters are generic, the conversations you overhear don't tend to refer to anything in the evolving plot; the fact that the stronghold is in flames, the mountaintop is in the middle of a snowstorm, or that Himiko is dead and the sun has come out for the first time in months (to take a few examples from play). Pity. I'd love to hear what the excellent voice actors might be talking about if they realized they are free to leave the island and their entire cult was a pointless waste.
The highlight so far was listening to the poor Solarii looking at the elevator you broke to get up to the General's tomb and grumbling about how he has to fix everything on this junkyard island. That's an entire mini-scene -- recorded dialog, encounter -- you'd never encounter in strictly linear play. A more spectacular example is if you go back to the first camp with Roth after the rescue plane crashes, you find the plane strewn over the campsite and Solarii busy taking it apart for salvage.
Another weird little break from reality I've noticed. This is a scaling problem. What I mean is, game mechanics often have to satisfy both a single use, and multiple uses, and it is impossible to optimize for both. In the Civ games, it is fascinating to learn about the origins of crop rotation, to send you people out to find and quarry stone and build a road back to your growing town in order to build a granary...but by hour six of the game, with fifty cities to manage and a technology tree longer than your arm, it becomes painful clicking through the long build list and trying to manage tens of idiot workers.
In Tomb Raider, one mechanic is to allow you to rifle bodies for a few bits of extra salvage. Another is to gain small amounts of ammunition in those same searches (which you unlock by purchasing the appropriate skill). Another mechanic is of course limiting maximum ammunition carried so you can't just hose everything. A last minor mechanic is one that limits the number of entities on the map by getting rid of slain entities over a certain number.
The result, however, is that you end up searching the bodies during the fight. Especially if you are trying to cherry-tap, using only the pistol to get through one of the big set-piece battles; the only way to reload is to take a few bullets off dead enemies on the run. Which is pretty credulity-straining as a concept.
Because searching happens over and over in the game, it is made a very brief action (having a five-minute animation played every time would be annoying). Also, the AI has lag. Some of it may be programmed in that way, and some may be a result of a mechanic that says if you are "scrambling" (aka moving around with frequent taps of the "dodge" button) you are harder to hit. So you can pretty much run over to a body and perform a search while under fire; it will take the AI that long to figure out where you went.
These same limitations in the AI also leaves opportunity for a more interesting combat style for some levels. The game really wants you to hunker down among cover and snipe. Instead, I'm having fun running right up among the attackers, getting inside their lines and hewing away with the axe. They get so confused they have trouble figuring out which way you went, and it takes them long enough to switch from ranged weapon fire to hand-to-hand you can usually get crippling blows in before they can react properly.
I did get killed a lot doing this, but it was a lot of fun.