I have a niger and a valentini in a tank together, and they get along fine. I have a Huma Huma (in a different tank), that is very aggressive. He is with a stars and stripes and porcupine puffer, and a domino damsel. I have tried to put others in the tank with them, but the Huma trigger attacks them relentlessly. He will often snap at the porcupine as well, and that puffer is easily 4 times his size. He will soon have a tank of his own. He does get along with the damsel and stars and stripes just fine
. Point being I would not house a Huma Huma with a valentini, my valentini is not aggressive at all...just cruises around, so I can't see him fending for himself very well. Of course all fish are different, just my experience and two cents.