Wolfgang,
Last question first: I don't think there is much out there. It seems that most tool developers who might be interested in this area are oriented towards Windows (and often specifically MS tools), anything but MS (and often Java specific in that camp), or Mac. I'm sure there's others, but I haven't run into anything like what you want from them.
As to the rest, I wonder if you could somehow make use of an XMI export from EA. This could be produced from an automation tool. [Remember that EA only reads and writes XMI data (versus the XML project interface) via files, not memory streams or strings.] I suspect, without proof that the export contains all the information EA holds, so might give you enough to perform whatever downstream manipulation you need.
You'll have to come up with your own representation of tab controls and the like. Perhaps you can use Shape Scripts, but you might have to wait for the documentation to be updated - I know Sparx is actively working on that. The hitch is that I do not know whether EA will allow scripts for UI elements.
This is not so bad, since you will would have to deal with this problem at some point. If you are working on a general tool you are certain to encounter UI elements beyond those EA handles, and a general way of handling them should be one of your early priorities.
BTW, you should also note that the Tab control in Access (at least up to 2000 inclusive) is different than that used elsewhere in the MS world. There are some other controls that are also different but the Tab control is one of the more profound. You would have to deal with that at some point regardless of visual aspect issues.
Sounds like you have an interesting project. Regardless of the work, there are significant advantages to managing this kind of information in the same tool as the rest of your model. Keep me up to date if you proceed further.
David