Does anyone know the name of thehardware generally used for this purpose?
Not really, but you can glean some hints from here:
Seems to me there are a few 'tiers' of 'fanciness' in using multiple projectors together:
* Manual operation using a remote control unit, possibly with a dissolve function
* Basic automated operation with a rudimentary programmable control unit that e.g. alternates between both projectors
* Fancy custom automation using a computer of some sort and a digital interface between the computer and the projectors.
There's a thread here on Photrio that was last active only a few years ago that featured someone who got a couple of Kodak carousel projectors (IIRC) to work together, I believe even using some kind of computer control - so that would be the 3rd option on the list above. Sadly, I can't find that thread ATM.
Given the notes on equipment listed on the kxcamera website it seems that the interfacing was at least to an extent standardized and some of the misc stuff that would work with Kodak projectors might also work with the Hasselblads, perhaps after adding the required interface to the latter.