See title. Data filed under Deleted Artist is not easily accessible to users, nor is there any good reason to store anything there. But it is possible to move entities there via DA's MBID http://musicbrainz.org/artist/c06aa285-520e-40c0-b776-83d2c9e8a6d1. Luckily, it seems like I'm among the only ones who tried such hijinks.
Furthermore, merging artists into Deleted Artist creates a bizarre situation probably best understood through examples.
MBz Test Artist: http://test.musicbrainz.org/artist/7e84f845-ac16-41fe-9ff8-df12eb32af55
Nagios check release: http://test.musicbrainz.org/release/1735e086-462e-42c3-b615-eebbd5e9f352
The test artist didn't get merged into Deleted Artist when the merge passed, but it now gets treated just like Deleted Artist. Among other things, that means the artist page displays a Page Not Found. But through the existing releases, one can see that the artist still exists.
The second phenomenon could be hard to fix, so I suggest that we just check that no moves and merges toward Deleted Artist can be entered into the edit system.