No. Eventually the Marines would be destroyed.
They would win as long as they had fuel and ammo, then lose.
Even if they could reload ammo, recharge batteries, and make their own lower tech weapons, the logistic challenges of staying ahead of consumption would eventually cause them to be overwhelmed.
The Romans, after learning that pitched battles end in disaster, would cut them off from food (scorched earth) and use guerilla tactics to disrupt them. (Read about Fabius Cuncator - Fabius the Delayer)
Eventually, logistics and friction would grind the unit down and it would be destroyed.
However, Romans are nothing, if not pragmatic. The Marines could become wealthy Roman Citizens if they decided to join the Republic or Empire and employ their weapons and expertise on the Romans’ behalf.
The Marangian Guard. :)
Just think of it—the Roman standards topped with the Eagle, Globe and Anchor...and the “SPQR” replaced with “USMC”....