The answer to be found in this thread seems to very much vaguely depend on the level of need to integrate Gallery and eZ ... <i>aka more details please</i>, what do you need to provide?
I think you could run gallery within a frame or iframe but if it was me doing the work ... I might try to place a stock gallery into an ez module extension.
Then based on my gallery experience :) I would consider re-configuring gallery's own internal settings to use the most trimmed down feature set. This only takes a few minutes and makes gallery very usable inside of another existing application.