If there was a DVD rip available you would also see it on anidb.
Not fully true. While people make an effort to keep AniDB updated, there are releases out there that aren't included in AniDB, usually self-rips/encodes or lesser known non-english groups that still release with engish subs but never bother to add it to AniDB.
Besides that, sometimes BBT users have the DVDs, but never bothered making an encode because no one seems to show interest. It's not a common things, but has happened.
So, requesting stuff not on AniDB isn't necessarily a waste of time.