There's surviving, and there's thriving - tardigrades could probably hang out in a Mars crater for a long time, but what they'd need to sustainably live on an alien planet is something to eat during the periods where conditions are right for them to thaw out. If there's nothing for them to wake up to, they won't be making anymore tardigrades.

Say, a very hardy algae that could make it in some suitable microbiome - like humid cracks in the rocks, or a fungus that could hang out in underground caverns shielded from UV radiation.

If we are trying to seed a place with life where we can't reliably go ourselves, it seems important that the 'colony' should become self-sustaining immediately-ish.

(Also I find the idea of launching swarms of micro-pods loaded up with hardy, tiny lifeforms endearing - like throwing seed bombs over a tall fence :) )