So say I put Talabheim Detachment in play as a development, could I use his ability to return him to my hand? I realize that it would effectively give away what the card is, but I thought it was worth asking.

In case you don't have the card in front of you, it reads: Action: Spend 1 resource to return this unit to its owner's hand.

No. You can't use abilities of cards that were played as developments.