It doesn't seem unreasonable to try, but the devil is usually in the detail
when you do this kind of thing. Personally I would try to borrow the
necessary hardware and experiment before spending anything, and I'd probably
try to find out what the device manufacturer had to say about it.

For one thing, the wireless printer adapters that I have seen are a bit
picky about which printers they will work with. With a multifunction device
with print and fax capabilities, there would typically be two print devices
on a single connection, and I don't know whether these adapters can cope
with that. I wouldn't expect other devices in a multi-function printer to
work wirelessly either (e.g. memory card slots).