What happens when two SRVs try to pull at each other?

Probably not a lot. Again, it depends on what those two ships are doing. If one is stationary and the other is moving around a lot, that one is having to use its power to move around. The other one is having to use more power to try and tractor onto it. I don't know if there's an answer for that.

I think they're picturing two SRVs, shields down, locking tractor beams on each other and going in opposite ways. Then it becomes a question of power management and throttle management and stuff like that.

It's like tying two people together with a bungee cord the same way. It depends on what you physically do. The bungee cord becomes irrelevant at that point.