Out of the box, Opus should view (or not view) EPS files the same as Explorer, and both will probably depend on a 3rd party component to decode the files as neither has EPS support built in. Any viewer which works in Explorer should also work in Opus.
(Some may only display the first page. I don't know if any exist which act as a full document viewer for EPS like there are for PDF files, but I've never looked so there may be one out there. Maybe even one of the PDF viewers does this.)
In terms of Opus-specific plugins, Ardfry's "Adobe Illustrator, EPS, INDD and PSB thumbs/viewer" plugin may be of interest. I have not personally used it with EPS files so I can't say how well it works with them, but it's worth investigating. My understanding is it will just provide a still image of the first page, not a full document viewer.