Not 100% sure about built-in OS support for the 111s, but I put a 110 from NewEgg into my G5 late last year and it worked without issue.
If you want it to look just like the built-in drive, you'll have to pull the little front strip off your built-in drive and put it on the replacement after you remove the wider strip. It wasn't obvious (to me, anyway) that that strip was removeable, but it pops off and on just like the larger one that comes with the new drive.
I'll work fine if you don't do this, but if you do (and remove the eject button, which is easy but totally unnecessary) it'll look exactly like the stock drive.