I've been google scholaring these for some time now (links shared below). Many report Bryopsis when they're juveniles, and they become more accepting as adults (maybe?). I think the AA article described the slug methodical om noming method to save chloroplasts and move them up to their leafy parts for bonus energy via photosynthesis. I'm highly skeptical of any dead algae waffer/sheet/whatever doing that service, though I have come across reports of success with dry store bought foods...still skeptical... Just have a hard time grasping the slugs bringing dead algae back to life and putting it to use.
In addition to diet you're probably going to want to guard baffles, overflows and powerheads to avoid some blending and/or sump rides. Recommend hitting the clownfish / anemone boards or searching for anemone guards. No one likes a blended nem, so there will be some useful suggestions on how you could protect your slug.
**Disclaimer - I am no expert. Never owned one or ever claimed to have success, just sharing some links n' opinions. Probably included some ranting too
http://www.advancedaquarist.com/2004/10/inverts
http://www.seaslugforum.net/factsheet/elyscris
http://seaslugforum.net/find/11846