Yeah. Can you give someone, say, a pair of warp pistols and have him use both of them at the same time?

If yes... w00t yea!

If no, I guess I'll have to use a couple hundred of those acid grenades now, won't I?

You can't use two weapons at the same time sadly. It may be possible to add in a mod though? Not sure...

I could be added, but the way I thought it can be done is somewhat odd. You would have to define a 2 handed weapon and you would siply copy paste the weapons statistics, double the number of shots and rate of fire (twice as fast) and probably lower the accuracy just for balance. Problem here is that you would have to carry an independant weapon if you wanted a single handed one, animations should be added or else it would look weird.

Bottom line is, you would be adding a new weapon rather than making them dual-handed. And in that case I would rather see a Warp SMG