I had a family member with a home bipap machine. Was told something about a valve was different and thus why the hospital mask we brought home wouldn't work. I don't think every machine requires its own mask, but could see there being a few different kinds. I don't know, will defer to the RTs in this thread on that one.
As for policies and liability:
RTs don't mess with home bipap because RTs get to bill for their services unlike nurses. So while we're tucked into the room charge, everything the RTs do can be reimbursed. But if they're just helping with home stuff, they're opening themselves (and the hospital) up to liability for things they aren't being reimbursed on. What hospital is going to allow that?
When nurses help with non-hospital approved/biomed checked equipment, we're also opening ourselves up to liability. Do you know if the machine has been maintained? (Especially if you can immediately see problems with the mask/equipment, what else is going on with it that you can't see?)
Anytime we have patients/families that want to use home equipment they bring in, it has to be checked by our biomed team first (which can at times be ridiculous, things like a feeding pump are pretty obvious when they aren't working right, but with breathing equipment, not so obvious so I'd agree a good thing to check) and generally we can't touch them, patient/family has to do all the adjustments. Unless there is a really good reason the home equipment is superior, using hospital equipment is just easier and avoids all sorts of liability issues.
The bigger question is why on earth does CPAP require transfer to ICU? It makes sense if a patient out of nowhere is requiring it (because why they suddenly need it likely requires close monitoring), but on a patient that regularly uses it at home?