Basically if you can get a working compiler environment on the systems then it should be possible to compile the neccessary bits on it.
Thats a bit of work though as you need not only compile mt-daapd on it but also a couple of libraries and such need to be installed first before compiling mt-daapd will work.
Other than that the speed and ram will certainly suffice. Is the energy consumption small enough to recommend running these units as servers. Everything using >30W you should forget immediately. The NSLU is like 10W usage.