CouchRest_Model is a lovely way to handle CouchDB calls from without your rails app, it provides an Active Record like interface to your data.
In a project I am working on at the moment I am using both CouchRest_Model and Active Record at the same time, which isn't a problem at all and they normally don't stand on each others feet.
I say normally because one time when it can cause issue is whenever you are generating migrations using the command
rails generate migration myMigration.
You may find that if you run this you will get the following error;
error couchrest_model [not found]
This is because CouchRest_Model assumes it is the default ORM, which is fine in the app, but not find for migration generation.
To get around this we can add a flag to our migration command;
rails generate migration myMigration --orm=active_record
This will allow the migration to generate as expected.