As it is currently, there is absolutely no reason to use any composition of classes besides 4 marauders for HM operations. Not only is their dps excellent, but with 4 mara's the group can roll "constant" bloodlust to maintain max group dps. The best solution is to put bloodlust on a global cool down for the group analogous to battle rez.
You know what if you want to bring 4 sents into an op go right ahead. It is however advisable to bring 2 melee and 2 ranged for many reasons. The first is that commandos/gunslingers bring a raid wide armor debuff. Second is that TK Sages and Sab. Gunslingers are the aoe kings. While I know that sents have some aoe capabilities, TK Sages will NEVER run out of force and we can spam the **** out of force quake. Also when we force quake we almost always get a Tele wave proc which is even more aoe damage. Sab. Gunslingers are pretty much all AOE and have many ways to get energy back fairly quickly. Also on a personal note, I find inspiration (w/e the sith equivalent is) makes things too easy. The content is already easy enough even on HM; why make it easier? I run an 8 man HM ops group with the following dps and we do just fine:
Tanks: Shadow and Guardian
Healers: Commando and Sage
DPS: Guardian, Scoundrel, Commando, and Sage
The last reason is that melee always take more damage due to so many conal and frontal boss abilities. In 8 man ops, both tanks can just guard the melee (if only 2) and make things easier since most of the time a really skilled sent (which believe it or not is hard to find) will pull more aggro than a ranged.
Without any inspiration we have never hit enrage timers even in 66/69 gear in HM S&V when it first came out. All I can say is that it is personal preference so what you want to do is up to you. It doesn't hurt to diversify though.