Yes, of course.

I'll be looking very closely at any metalborn abilities and combinations before approving characters, and it would be good to have a balance of abilities on the team. So yeah, not everybody can be an allomantic tank destroying everything in their path. 
Aside from Miles, there won't be any double golds around, and since this is set five years before AoL, he will still be out in True Madil doing his job as a lawkeeper and not participating in this game (probably).

Coinshots are cool, though, and you could even play a twinborn. They are very rare, but, on the other hand, the 17th Squad are rare and talented people.