Eble vi intencis diri: "Sed ĝi manĝos ĉiujn de la vegetaranoj."
I was constantly flubbing -us with -os until I learned the mnemonic: "Was is, is was, os will be, but us could." Then there is the "Don't follow da with la" rule. (more of a general suggestion, but it seems to work)
After all of that I say keep plugging away. Mistakes are how we learn. (And the Good Lord knows, I make enough of 'em.)
In French using future instead of conditional indicates that the probability that it will happen is high. http://www.tolearnfrench.com/exercises/exercise-french-1/exercise-french-195.php and in Spanish if something would happen but doesn't you could put conditional, but if the probability is high that it will happen you could put future. http://www.dummies.com/how-to/content/choosing-between-future-perfect-and-conditional-pe.html So, using the conditional implies, if you hired a bear which is unlikely, while the future concentrates on the bear already being there. Personally, I don't think it is so likely that the bear will eat any people, so I would use the conditional. You even use the word "might" which does not indicate a "high" probabability. "Ĝi ne manĝos iu." "Se vi dungus urson, li manĝus ĉiujn de la vegetaranoj kaj ĉiujn de la malvegetaranoj esceptinte ke vi donus al li plialtigo kaj liberdonaco da mielo."
(I hope I did that right. I meant: It will not eat anyone. If you were to hire a bear, he would eat all the vegetarians and all the non-vegetarians unless you give him a raise with a bonus of honey.)