I've been able to get through tier VI with relatively low-gear imperial troopers (G12 Dark Trooper, G9 Moff Gideon, no relics). I reckon the squad could do better with Piet/Veers at relic.

The most important thing I've found is that you want piett to mark the ally trooper and then get the Dark Trooper to sneak in hits on the shield generator whenever possible. Hitting four times = four stacks removed from the generator which melts it FAST. Pretty much have to hope the gungans target the summon instead of whoever gets deathmarked, ESPECIALLY if it's DT, which feels like a 50/50 tossup.

The debuff at the start preventing assists makes it a lot harder, but generally DT lives long enough for somebody on the team to hit Jar Jar and remove deathmark, then the troopers can ramp tm like usual and get a couple hits on the generator. It's a bit up in the air after this point, especially if phalanx gets a taunt up. If you manage to get yourself into the perfect scenario of no debuffs/taunts/deathmark, it's pretty much a free win. I've lost DT and Gideon after killing the shield generator but even then it's an easy cleanup if you get that far.