you what's safe to delete. In one instance, the Opera browser has (had?) motif dependencies. However, because Opera is not a Debian package, anddoesn't actually fail to install without the libmotif package, deborphan willhappily tell you that that the libmotif package is on its orphaned (no dependencies on it) list.
Just for information - Opera is being distributed as a .deb since at least version 6, and at least the current version I'm running (9) doesn't have any motif dependencies. It probably hasn't for some time because I've been using it since 6 and can't recall having thrown out motif.
--Daniel