Web UI + Command Line is a use case that RTC developers have made a conscious effort to cover common workflows - but without knowing much more of your process I can't say for sure if there are holes in specific use cases that you may have.
So my short answer is "yes, you should be able to do most things with just the CLI + Web and No, Eclipse is not a necessary requirement to do work".
To clarify for my long-winded answer - I am not sure what you mean exactly by "do their building and workspaces on an AIX server".
1) By building, do you mean launching RTC Build definitions? That can be done via the web.
2.i) have never used AIX - so maybe my next paragraph will make no sense but... from my understanding I have some ideas with caveats:
2.ii) By building (and workspaces), especially when Eclipse is in mention... do you mean java compilation of source loaded on disk? (Because sometimes we think of Eclipse as only a java IDE...) ... and when you say AIX server, what do you really mean...? The CLI and Web are "clients". Would your loaded source and CLI client be on an AIX machine? By the context of your question it sounds like when you say "AIX Server", it means your "client" is a "remote machine that is AIX and therefore hard to run Eclipse". If that's the case, (and to contrast, we could say these clients on an AIX "server" could be talking to an RTC "Server" which happens to be running on Windows...), then I think you already have a way to log into your AIX (in order to run your CLI) and so you should be able to use whatever other local tools you want to do your local compilation ("building").
3) I'm not sure what you mean by "Eclipse IDE to combine both sides of RTC". What are the two sides?
3.a) If the sides are server vs client, then No, eclipse should not be required. Your server is whatever your webapp container is and your client(s) is your CLI + Web
3.b) If the sides are CLI vs Web, then No, eclipse should not be required - except for if you have some workflow that we have not thought of that happens to be feature rich in Eclipse but didn't get covered by the other clients.You would have name something more specific for us to check.
3b) If the sides are "Change Management side of RTC" vs something else... then maybe I'm just getting confused with terminology. I usually think of RTC is the "Change Management"(ccm) side of Jazz(jts), and there are the other jazz family products (Requirements Composer, Quality Manager)... and I know less about this family of integration to make a helpful comment.
