Certainly for AI scripting, you can use vectors. I don't know anything about RMS here. They're just like any of the other builtin types (int, float, string) except that initialising them is a bit more difficult as you can't just "write" a vector in the same was as you can a string or number. Well, XS won't accept it, anyway.
vector something = cInvalidVector; // XS variables complain if you don't initialise them
Fairly sure the invalid vector is defined as (-1.0, -1.0, -1.0) but it's probably not something that's worth counting on.
Probably more usefully though, is this:
vector something = xsVectorSet(1.0, 2.0, 3.0);
Documentation for various defined XS vector functions is in Mythic Freak's handy page in the xs.xs section. If you want to do stuff like squared distance comparison or anything else snazzy you're going to have to write it yourself though.
(I don't even know if it's worth writing squared distance comparisons or just using xsVectorLength() actually...)[This message has been edited by Loggy (edited 09-30-2015 @ 06:58 PM).]