Actually, on looking through the Omnibus a little more, there's a thread where they're talking about the increased tileset limit in 1.69, and a couple of people (Axe Murder and Ivanovic) say that the maximum number of haks allowed in a module is 50. The next response in the thread is from Craig Welburn (a Bioware staff member) who says:
'The number of hak packs allowed hasn't changed from 1.68.
Although now I believe the log file displays an error message if the game tries to exceed the maximum number of hak paks it can load.'
Since he doesn't correct them (and is talking about patch 1.69), it looks like a maximum of 100 tilesets and 50 hak pack is the answer to your question.