Tomlinson Never Stumble Ability Off The Bench.

Damn I was really pumped to get Marino to Tier 5 Go Deep.  Wish I had the coins to buy a good RT with the double go deep chem.

No, not unless you have someone else starting that does have the chem. So, for example, if you started Barry Sanders or Travis Kelce, then LT would still have the Never Stumble ability.

Not if it's not active by another card that starts

If you have it activated in your lineup by someone else, sure.