I don't want to harm poor furry Ysalamiris ...
But you have to bring sacrifices, for the good of the Empire - and the Ysalamiris would surely willingly assist our cause, if they could understand it. Anyway, it's for their own good, it protects them as well ... just think of all those nasty Ewoks and Wookies whose greedy maws are salivating constantly when thinking about roasted Ysalamiri steak!
And no one complains about rebel scum, forcing innocent Taun Tauns to carry them on their weary backs - a rebel would cut one of those poor beasts open without a thought, just to warm himself a little with it's steaming guts! And that's not just a horror story - it's true! The depraved followers of the Rebellion have actually been seen doing this!
Imperial Troops, in contrast to this, offer their own strong backs to carry the Ysalamirs safely and comfortably around so that they can see the galaxy from behind the broad shoulders of a brave stormtrooper.
But back to the point
The point of introducing jedis/sith would be of course to add diversity. They shouldn't be able to do all the stuff a jedi from the Jedi Knight series could do, as that would be clearly overpowered. But even some limited abilities ( as I proposed: force push, chain lightning) could be a nice touch. The question of how powerful they actually should be is, of course, linked to the amount of jedis on the battlefield. If jedis are just another special class for some levels (for example, in the form of an imperial royal guard in a Coruscant/ Death Star Level ... please not on every level, this would lead to a ridiculous jedi flood) - which would be actually a very nice idea and perhaps my favourite solution of how to include jedis - they have to be balanced to be just as strong as the other classes. Which shouldn't be that much of a problem. If you limit their available numbers per level or make them an "earned class" they should be a bit stronger ...(by the way, Royal guards could surely be used for this role, too) and a VIP jedi (being a possible mission target) would have to be even stronger. Not such lame invincible entities like the ones we have now, who just hang around hacking at hapless people with their sabres.
These are all interesting options ... but their are even more exciting things which should be added to the game first
P.S.: Destroyer Droids are surely tough ... but as they are sitting targets once their shield is down (a single rocket /thermal detonator may be enough) and not very mobile, I think they are actually quite balanced.