My heritage White Holland toms are competing, now, for who gets to be Alpha male, as they are growing up. Since they were almost all hatched at different times this year, spring through summer, it isn't much competition as the larger ones usually rule, at least until the younger ones catch up. Every once and a while, while free ranging, a Rooster will approach a young tom and want to fight, being the chickens have been around longer. Roosters, being what they are, will even try to mate with one of the turkey hens. (Let them try that with a 30# turkey! She just has to stand up and he will fall to the ground and walk around embarrassed, LOL. When a Rooster picks a fight with a younger turkey, it doesn't last long at all, before another turkey or two join in to put the rooster in his place PDQ! You could have this sort of thing, with the midget and standard size birds, I suppose.
I would think, it would be darn near impossible, for a midget male to mate with a 30 pound Holland or a 40 pound Holland tom to mate with a midget hen. 12# with 30# or 40#with 10# either way would not, in my opinion, match up. I do agree with Oregon Blue though, the midget turkeys could get badly hurt, or in the least get their egos really bruised!LOL