Gluu is an IDP itself, and in fact bundles Shibboleth IDP.
If you are OK to operate your own Gluu IDP, then you can integrate with your partners using our inbound SAMl documentation:
The idea is that even if users auth at external Shib IDPs, you still need a way to identify the users locally, meaning you need somewhere to store the user data..that would go in your gluu server.
Im closing this ticket because I believe i have satisfactorily answered the question. There are a lot of existing tickets about getting this working properly.
If you want to hire a resource, we could introduce you to a oartner of ours. Email me directly if you'd like a referral.. will at gluu dot org.