I coated my subframe with por15. Some places look brand new while a couple spots don't. Can I sandblast that area and recoat? Or should I sand on it some and just coat over it?

I wouldn't worry about it, but its the flat spot between the the control arms and where the radiator support bolts. This spot will be seen very easily.

just sand it a little and sand it an recoat the entire area. It will even out.

The directions say to use there primer for recoating....

Yeah you probably want to use their primer for painting over dried Por-15, unless you bring it back down to bare metal in that area:
http://www.por15.com/images/TCQ_Tiecoat_300.jpg
http://www.por15.com/prodinfo.asp?grp=TC&dept=3

Today i just finished my sub frame also. Cant wait to see it tomorrow, thank god the motor is out and especially if your trying to run new gas line (went in like a champ).. Oh don't get any of the Por-15 on you, it doesn't come off...
Go thread and great advise on that primer first before recoating.

I've gone both ways with this. I unfortunately scraped the POR to bare metal in a couple places by accident. If this happens and you POR without primer you will always see the line where the lower layer ended. I didn't bother with primer on small spots. For larger areas I'd highly recommend it. If you're just trying to smoothen the look, then I'd sand softly until you get the smoothness you like, primer lightly so you don't get a layered effect then recoat lightly. Otherwise you might just see the layers. Did you use their marine clean to get the grease off first and then followed it up by Metal Ready? If you didn't at least use Metal Ready, then there is a strong chance that the POR is just sitting on top of the metal without actually having bonded to it. If you scrape too far it will begin peeling off in large pieces like sunburned skin. That's why I say sand lightly.

Good luck,