Hello!!
I was wondering if there is any way to access the data an SSRS report pulls together?
I’ve tried looking into it, and the only option I’ve come to is building a BAQ that mimics how the report pulls the data. However, even with looking at the report in Report Data Definition and Microsoft Report Builder, I’m not sure if I’d be able to accurately replicate it (particularly all of the links, relationships, and calculated fields).
All the data that is pulled for the report is stored in the SSRS Report db. Since you are on prem, you could always use SSMS to run a query against it.
The data in that report database is temporary and only lives for the ‘Archive period’ specified when you run the report.
Re-reading your question - is this one-time/one-off situation? or do you want to access this data regularly? because it sounds like you’d like to build a BAQ to pull the same data as the report.
If so, you are correct. Epicor does hide a fair amount of relationship & calculated field code inside the RDD that is hard to reproduce exactly unless you are very familiar with the data. Most of us just work it out after much hair pulling and searching on this site. 
If your SaaS you can’t get to it but otherwise what the above have said. You can set the archive period and then use the GUID to query the SSRS DB .
This may help. Depends on your version which is not listed in your profile.