Is there a way to play with a friend on the together mod and play the ultra mod together or is that not possible?
its not possible sorry
Ultra mod is based on update 19 so that's about 1.5 years of differences in underlying game structure.
It is possible to make mods to selectively mimic most of the interesting parts (characters, weapons?) of it though.
I'd think that at least someone of people asking about this would have enough programming experience to get on that.