I think the ruling is that you can't activate this card during the turn you summon a monster.
At least that's how Vision Hero Witch Raider's effect is ruled.
Witch Raider has a similar restriction in that her effect cannot be activated if you summon a non-HERO beforehand.
I had DNA Surgery on the field, activated Stray Lambs, they became Dragon type. I had enough dragon monsters on the field and in my hand to activate polymerization and summon 5 Headed Dragon, but the game would only let me set polymer.. Is this an oversite or a bug? Tokens count as monsters so there is no reason for this to not work as far as I know. There is only 1 DNA surgery in the game so I can see the devs just forgetting to test this interaction or something.