That does look interesting for those wanting a powerful image/media manager and decent image gallery, and the fact that it is an ASP.Net user control suggests it might be relatively simple to wrap it as a mojoPortal feature. After a very quick read I note that it can use any membership provider, uses resx files for localisation, and several other things that sound compatible with a mojo site.

However, note that GSP was previously sold as a DNN module, but they have now pulled the plug on this, for reasons explained in this blog post:

http://www.galleryserverpro.com/blog?title=Gallery-Server-Pro-DotNetNuke-Module-History-and-Roadmap&id=5593054765489074428

Some of those reasons certainly do not apply to mojoPortal, but some may indicate that this integration may not be plain sailing.

I don't know enough about Entity Framework Code First Migrations to know whether there will be real problems in that area, though it certainly doesn't match the existing mojoPortal pattern. My guess is this aspect might "just work" with the necessary additions to web.config for the entity framework, but only if using SQL Server or SQL CE, as that is what the GSP code supports, i.e. without using the standard mojoPortal method of creating/updating the data structures.

I've just noticed that others are attempting this exact same integration, e.g. see this recent thread:

http://forum.galleryserverpro.com/yaf_postst7241_Integrate-with-another-CMS---Not-DNN.aspx#post17059

It will be interesting to see where this goes!