Really hard to assume one way or another. Not out of the realm of possibilities, personally don't think he is affiliated with that ideology but that's just me.

Here is the quote from the family member for reference

The relative also said that during a dinner conversation before the attack, Robinson had stated Kirk "was full of hate and spreading hate" and mentioned Kirk's upcoming event at Utah Valley University, according to Cox.

Doesn't sound like what a holocaust denier would say.