Yes, you can tap tribal permanents to activate Kumena.
Any ability that refers to a creature type without specifying that it needs to be a creature can use non-creature tribal permanents with that creature type. For example you can also grab Merrow Commerce with Seahunter.
January 29, 2018 6:58 p.m.
Also, just in case it ever matters, Merrow Commerce will get +1/+1 counters if you use Kumena's third ability, but since it's not a creature, they will largely be irrelevant, but should be tracked just in case your opponents play a Thief of Blood, Daghatar the Adamant, Opalescence or some other similar card.
January 29, 2018 11:49 p.m.
Daghatar the Adamant won't matter though. It can only move counters from creature to creature.