Yes, there was a version for evaluation and tests.
The GSh-6–30 was used in an effort to change the board cannon for the SU-25 Series.
Overall, the air frame of the Su-25UB (two seated trainer) was used to have more room for everything, more including ammunition.
The Su-25 T-8M configuration with the 6 barrel 30mm gatling gun, and the Su-25 TM configuration with a single external GSh-6-30 (AO-17A).
There are very few pictures of the Su-25 T-8M. The only one you see is mostly the 02, although many have suggested that at least 5 planes in this configuration have been build, flown and tested, all were labeled with 02.
The Su-25 T-8M or some of those 02’s were actually tested in Afghanistan.
However compared to the A-10, the focused weapon of any Su-25 was not the gun, but everything else, especially guided and unguided rockets.
The gatling gun simply never made sense for the soviets.
After figuring out that there was no need for more room in the fuselage all other following Su-25 including the Su-25SM returned to the more slim version of the airframe from the regular Su-25.
Only the Su-39 (Su-25TM) is again using the larger Su-25UB Airframe for more avionics and fuel.
Looking at the parameter of the Gun for the A-10 and the gatling gun for the Su-25 T-8M (also used on Mig-27M) shows similarities and differences. Due to the fact that the GSch-6-3 is driven in a gas actuated mode, it does not need all the auxiliary systems as the GAU-8/A. The recoil of the GSch-6-3 is even worse than for the GAU-8/A. While the Su-25 could still handle it the Mig-27M had it mounted obliquely to absorb recoil better.