Title says it all.
Look at this. This is the USUM map. Look in that tiny island on the Top-Right corner. That's right, PokéPelago. This question is asking if Mohn, the owner of PokéPelago is the leader. As we know, Evil Team Leaders always is against you. Mohn is just cheering you on. Not only that but, if it is that means he has to take care of PokéPelago AND Ultra Recon Squad at the same time. They do share similarities with the blond hair, but it's just like saying Pryce is Guzma. So personally, I think It's Pretty Unlikely I may be completely wrong but this is still a possibility.
Source: This Image (Or if you're too lazy to go to the link just look at the top of the answer.)