Once you let in the DDR, how can you reasonably deny Austria, for instance?
I can see that a more assertive Russia might have successfully demanded than no state bordering Russia be able to join either the EEC or NATO (especially the latter), but if they allow reunification of Germany and thus the DDR's entrance into the EEC, it just isn't reasonable to prevent Austria and Sweden or (the successor republics to) Yugoslavia from joining. Let alone Ireland, which is nowhere near Russia.
What would happen, though, if the Baltics, Finland, Poland, (Czecho)slovakia, Hungary and Romania were prevented from joining the EEC?
My guess is that they'd join a larger, stronger EFTA. You might even get functional entrance into the EEC, even if not formal. For instance, OTL, Norway, Iceland and Switzerland are all part the Schengen area, without being members of the EU.