Can I use crankbaits on a 6'6 XF jerkbait rod?

I wouldnt, but nothing can stop you from

Nothing says you can't but most jerkbait rods are not XF and most crankbait rods are Mod. of Mod. Fast.   For me personally I like my jerkbait rod to be 6'6"  MH Fast with a soft tip and crankbait rods Mod. Fast.  The length and power depends on the bait and water depth. 

I used to fish cranks on a 6' 6" M/F St. Croix Premier. The heaviest tournament weight I ever brought in was fishing a squarebill on that rod. It may not be ideal, but you can do it. 

I agree with  bluebasser. I wouldn't throw a diving bait on it but a squarebill would work. Heck,I know a guy who makes custom balsa squarebills and is one of the best at it I know, and he throws them on a old Daiwa green handle jig and worm rod.... whatever works for you.

I would think that a 6'6" medium power, extra fast casting rod may be a bit too stiff but my 6'9" medium power, extra fast spinning rod works well with a #5 Rapala Shad Rap, but that is a spinning rod so it is softer than my medium power casting rods.