Tablebases are considered cheating. Like engines they provide solutions to what the best move in a given position would be. Databases are merely records of games played; opening books, while more authoritative, are still based on prior experience and theory, and fall in the database region.
All are banned for live chess though.
So far what I know--
-Opening Databases--allowed
-Middlegame chess engines--cheating!!
-Endgame tablebases--??
Would a tablebase be more related to a database? Or a chess engine?