I’m glad you like the app’s RAW conversions. When eGPUs were initially being supported, I did get a chance to test them a little bit with RAW Power. At that time, the only device we could connect was a MacBook Pro (because T-bolt 3 was not common on Macs). As I recall, RAW Power automatically used the eGPU when present, because for the most part, it lets Apple’s RAW engine decide which GPU to use.
The overall experience was that the eGPU wasn’t meaningfully faster than the discrete GPU in a MBP. That’s primarily because Thunderbolt is not as fast as the bus for internal GPUs, and the amount of data moving back and forth is quite large. However, (and I’m speculating here) it should be faster than an integrated GPU like the one in a Mini.
Again, my testing was limited to what Apple provided me at the time. Because the performance was not exciting, I did not end up investing in an eGPU for myself.
Long story short, given that it was a while ago and the time spent relatively small, my answer is “probably” for the first question (does it work with an eGPU) and “maybe” for the second (will it work with any eGPU). Sorry I don’t have a more definitive answer.