I have yet to actually get around to playing with FSP yet, (waiting for it to be added to the server I play on) but from what I've read, it isn't that its steam is incompatible with other renditions of the stuff, but that its steam pipes aren't regular fluid pipes like most other mods use to pump steam around. To this extent I think I recall reading that there is in fact a block in FSP that acts as an interface between the two piping systems specifically to allow usage of steam from other mods and vice versa. Unfortunately I don't know the name of said block, but surely it should be in the Esteemed Innovation Journal?
Very good to know! I've got both FSP and Railcraft in mine, I will have to take the time to play around with that.