It is possible to use a CVS project checked out using another CVS tool into Eclipse. A common concern for those migrating to Eclipse is that they already have their CVS project checked out on their local machine. You don't have to check out the contents again to create a project in Eclipse. When such a project is imported into Eclipse, the CVS plug-in may detect that CVS folders exist and auto-share the project. However, there are some instance were this does not occur and the project will need to be shared manually within Eclipse in order to enable the CVS Team menu operations.
To share an CVS project that was already checked out:
Team programming with CVS
Synchronizing with a CVS repository
Sharing a new project using CVS