This Link seems to suggest otherwise. Maybe you should try asking on the IPB forums (where you would get official support) instead of here? Just a thought.
You might also be interested in this thread, which covers what appears to be some fairly simple steps to make your IPB 1.3 forums compatible with MySQL 5.x. Maybe you've tried that already? I dunno...
Otherwise, if the IPB forums can't get it working for you, then you will indeed have to contact DH support and request you be moved to a MySQL 4.x database.
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