Oheka Castle -- No On Jeter ... Yes on Gym Owner

Derek Jeter ain't getting married at Oheka Castle in NY today ... despite serious buzz.

We know various high end vendors had been contacted to work a "Derek Jeter event" at the historic location this weekend ... but it turns out, it's just not true.

There IS a wedding going down at the Castle tonight -- but the groom is not a future Hall of Famer ... he's the owner of a Crunch gym franchise in Florida ... which is still pretty baller ... but it's not Jeter.