They were well and truly corrupt. Have a look at Impetus of War and the remainder of Twilight of the Clans.
I'd like to go on record to say that I don't think the Jaguars were TRULY corrupt or evil. For someone to be truly corrupt they have to KNOW what they are doing is wrong and then continue to do it anyway.
If you look at things from the Jaguars' perspective, the atrocities (from the view of the culture of us normal, well-adjusted people from the 21st century) in their history are all mostly
reactionary events to things that were perceived threats to their stability as a Clan, and the warrior caste was merely doing what they felt was the right thing for their Clan.
In Clan society, the warrior is king, and all other castes support the warriors. If the lower castes get out of line, the warrior caste suffers for it, and thus the whole reason for the Clan's existence hangs in jeopardy. Thus, if infractions by civilians aren't punished, others might do the same thing, and then soon the whole Clan will fall apart.
So, on Londerholm, the merchants revolted because they were being asked to give up their crops to help feed the warrior caste. When they said no, they were punished. Same thing happened on Atreus. On Turtle Bay, their new "civilians" revolted, and they were punished in a more permanent fashion (and I'd like to point out, the WHOLE Clan did not order the bombardment of Edo, just the local commander). Edo was NOT genocide; it was a punishment meant to make a statement, which it clearly did.
The only real problem (aside from our initial revulsion to the Clan cultural idea that civilian caste members are less valuable compared to warriors) is that the punishment the Jaguars mete out for these events seems to be a bit heavy-handed and unnecessary compared to modern common sense.
A truly evil group would go around belligerently and purposely killing people solely because they didn't like them or because they were different from them. A truly evil group would round up innocent people and gas them or bury them alive or toss them out of an airlock for no real reason whatsoever. The Jaguars fought their fellow Clans so often in Clan space mostly because they had few resources and few viable colonies for producing their own. This might be seen as belligerent, but it was not without purpose: Trialing for resources allowed them to survive.
They may be seen as "bloodthirsty" with all of their bloodletting rituals and such, but that's just culture, and no one dies from those rituals unless someone takes it a bit too far and someone really gets hurt.
The Jaguars' main fault -- if it could be said as truly being a fault -- is that when an infraction calls for a paddle, they bring out a sledgehammer (because clearly they don't have any paddles left and can't seem to win any Trials for more ;)). And when an enemy on the battlefield calls for a scalpel, they bring out a double-bladed battle-ax (because they're fresh out of scalpels too). I call this the "Lennie complex," where Lennie from John Steinbeck's
Of Mice and Men is so strong that if he picks up a rabbit to pet it, he will accidentally break its neck because he can't control his own strength and really doesn't know any better.
So yeah, the Jaguars were brutal, heavy-handed, arrogant, and generally unsavory characters as far as our modern sensibilities go. But were they all corrupt and evil? Not by a long shot.