Corruption eaters are medium-sized Aberrations with decent ability scores. They're also absolutely awful.
The first issue arises when corruption eaters attack. You see, their primary natural attack, a bite, damages them if they use it against something that doesn't have a Corruption score. What's that, you ask? Oh, just a very specific part of a very infrequently-used subsystem from a book almost nobody ever uses.
Even against something that is corrupted, these beasties aren't great. Damage-wise they'll be completely underwhelming, Tainted Exhalation (breath weapon that causes points of Depravity) is heavily dependent on getting multiple hits in against something that's Corrupted, and Purity Vulnerability negates the monster's main defense against 90% of foes.
Worst part? All of this is at the cost of 15 RHD. That's not worth the small amount of extra strength (orc is only three points behind by now), nor is it worth the abysmal natural attacks (most of which you must give up to use weapons anyway).
Even in a campaign where every random mook has a corruption score, this thing's only use is trying to get as many bites in as possible so it can unleash a semi-nova in the form of a weak AoE. It will barely contribute to overall damage, it will severely fall behind in versatility, and it will not even be able to tank better than a random dwarf knight (in fact, the knight can actually convince foes it's worth attacking, so that one may be better off).
There isn't a single PC class I wouldn't want to play over this one: -0 LA for sure.