If Chieftain Ufthak cannot attack (due to Feint, Thicket of Spears, Forest Snare, etc). does he get a token for that round? Official FAQ says CU gets token after resolving the attack. But what if he cannot attack?

I would say if he didn't attack, no resource for him. Same goes for Rupert in Carrock, no attack, no shuffling back Sacked!s.

He didn't actually attack so no tokens for him.

Chieftan Ufthak's forced ability adds a resource token to him after he attacks. Feint prevents the attack for the phase and therefor prevents the addition of a token.