I can't honestly think of any reason it would not work in mu-plugins, but to be honest I have not worked with that folder since before 3.0, when WPMU was separate from WP, so I can't recall what complications it had.
Give it a try, and let me know how that goes. If there is a problem with it working in mu-plugins, I'd love to know because at work (where this plugin was developed), they've expressed using multisite for the first time at this company (Sears), for a large upcoming project.
Let me know if you do or dont get it to work, I'd love to know, and If it doesn't work I'll do my best to fix whatever is wrong with it in a timely manner.
Thanks