From the Tank Commander entry (sorry, no page number due to digital version):
Since Pask is a Tank Commander he is covered under this sentence. There's also the contingency in the Warlord Traits table for Tank Commanders, and that Pask automatically has the Warlord Trait Old Grudges if he is selected as Warlord as per his entry. I'd say you're good going on teaching them that Pask can be their Warlord my friend k:The Tank Commander’s tank is a character, has Ballistic Skill 4 and can be
chosen as your army’s Warlord.