the main problem i would see with it, is the lack of melee vareity a sentinel would have, but considering shooting is supposed to have a bigger role in darktide it, might very well work as a boss that focuses 1 player with a multilaser into cover or targets a player for 3-5s then oneshots him with a lascannon if he didnt manage to find cover in that time. tho one would question if thats truly boss worthy probably would need an entourage of cultist to spice up the encounter.
Lorewise i think it would be plausable for them to have a sentinel they could have overtaken a manofactorum sector in the hive that produces military equipment so i dont see a reason why not.
Totally agree, not to mention I recall the lore stating that we’re also going for face actually traitor guardsmen so would presumably bring vehicles with them when they turned heretic.