SInce no one has answered this for you yet, I'll take a stab at it. However I'm not a GP expert, and in fact I've never even used the product.
That being said, GP uses SQL Server as it's data store and Tableau is great at connecting to SQL Server -- so there's a plus for you. Microsoft's SQL Reporting Services is sometimes used against GP's database to do reporting and that tells us a couple things:
- It can be done
- There are specific views in GP and/or "known" queries that can be written against GP to pull out useful and interesting data.
As I recall GP also includes a Microsoft Analysis Services cube that can be built on top of the data you're working with to do "hard core" Business Intelligence. Tableau also can connect to a cube, so you're good there, too.
So to summarize: Yes, I'm 100% sure you can do this and most likely get good results....but...No, you're probably not going to find lots of documentation / how-to information on same from a Tableau point of view -- GP is "just another data source" to us.
Hope this helps a a little?