Hi,
The answer to your question is technically Yes. But the practical answer is No.
The Dynamics GP SDK has provided table diagrams for each of the GP modules since way back (although I haven't bothered to check if they are still maintaining them with GP 2010 and 2013).
They are Visio files with nice pretty colorful tables, listing all of the fields, and with lines connecting the tables for the relationships. But there are so many tables and fields that they are very difficult to actually use--they are massive. Once you see one, your eyes will likely glaze over.
I have posted the GP 9 table diagram Visio files on my web site in case you are interested in looking at them.
http://www.precipioservices.com/gp/schemas/
But, instead of looking at a visual diagram, I would strongly recommend using the Table Descriptions under Tools -> Resource Descriptions -> Tables.
Open the Table Names window, choose your Series, then View By Table Physical Name.
Then check out Leslie Vail's excellent article on the GP table naming convention.
http://dynamicsconfessions.blogspot.com/2010/07/dynamics-gp-table-names.html
Once you understand how the tables are named, the names will no longer be random numbers, and you will typically be able to find data much faster and quickly understand the relationships.
Finally, Victoria Yudin has a blog post dedicated to GP table resources.
http://victoriayudin.com/gp-tables/
With those references and a few minutes of reading, you will have far more knowledge than a massive Visio diagram will be able to impart.
But let me know what you think and whether the diagrams are helpful.