I did it in Breakthrough, but didn't use the mortar. I just hung back slightly from where lots of my teammates were, and threw smokes towards nearby enemies. I can't remember exactly, but I think it might also count if you chuck a smoke near someone who is being revived. It'll probably be harder to do in Gauntlet but you might be able to adapt it.
The vehicle repairs one I just did naturally during matches. I guess you would need to wait for that vehicle mode in Gauntlet or hope people shoot at a vehicle you're the passenger in for RedSec.
I'm not 100% sure about what counts as an objective when it comes to the tracking in Gauntlet, unfortunately. Hopefully someone who plays it regularly can answer that one.