It is probably using the generic editor interface which I don't think has support for browsing aliased folders.
Nevertheless, if you know what the alias is you should be able to put %MG_ALIAS_PATH[NAME_OF_YOUR_ALIAS]% (I might be wrong about the special variable name here. Might want to double-check) into the raster path and it should work fine.
- Jackie
http://themapguyde.blogspot.com
http://au.linkedin.com/in/jackieng