I'll count tomorrow, but I think my Dak DOES use a 7-groove.
Of course...you could always use a 6-groove belt on a 7-groove pump.
If you don't know, Dayco's part number tells you a lot: it's three numbers, a letter, then a number. The listing for a 5.2 Dakota is 975K7...that is a 97.5" belt, with 7 ribs. (So yes, it looks like you're correct.)
But this helps you...because to use the Magnum PS pump with 6-rib pulleys, you simply need a Dayco 975K6.