I've got a Droid Eris that I've loaded the CELB Froyo 2.2 Rom, which is based off Cyanogen Mod 6. I know before that ROM Manager was basically useless with the Eris but I was wondering if it works now.
Depends on the Rom developers. Unfortunately no one but someone with an Eris or someone that develops for Rom Manager could answer this question. Just download it and see what you get.
The way Rom Manager works is the developers have to contact the Rom Manager team with the appropriate information that can then be added to the app. So Rom Manager team can only do so much to get Roms in it. Plus there are a lot of side conversations about how well clockwork recovery actually works when wiping, but I have never had a problem with this. And the issue of some Roms do not play well with Clockwork recovery either.
On the Evo Cyanogen is very good about keeping the ROM up to date in Rom Manager. Which is nice since it is updated nightly. I say try it again.
Remember that paying for it will give you access to all the Roms, so if you haven't paid for it you might not see some Roms that you would otherwise see.