Since you don't have an AMD graphic card you can't know this but Radeon Pro hooks itself (like the original AMD graphic driver) in between the hardware & software. It basically acts like a graphic driver, just with way more powerful tools. That the program can work this way requires it to be started (like the normal graphic driver) before the game.
Nonetheless I did some testing with the newly discovered method of starting everything as administrator. Now I can use the regular hook method and not the legacy one! Sadly it shares the same problem of being affected by Radeon Pro's settings. I feel bad that I have such bad knowledge about how this stuff works in detail, so all I can do to help you is to tell you that this problem does not occur with other overlays like Mumble or Radeon Pro's own overlay. Maybe it helps to know that it can work, so it's not an unfix-able problem.
If you need stuff to be tested on AMD cards and/or with Radeon Pro, feel free to use me ;>
Edit: This just came to my mind: As far as I understand Radeon Pro hooks itself in between the game and the driver, changing the commands and editing extra ones in it. Because mumble is not affected this could mean two things: It forces/uses commands who are not changeable by radeon pro, for example a forced LOD setting. Or it completely ignores/circumvents the hook of radeon pro in between and has a direction communication with the driver.
Edit2: fuck me, there is a warning of using radeon pro with elevated permissions everytime you start it as administrator but it actually seem to solve any problem. It looks like now I can start radeon pro after the game without getting an immediate CTD. Give me a few minutes to test if that actually solves the overlay issue as well.
Edit3: Woops I did a mistake while testing the latest changes, I was using RTST in legacy mode. I tried it with the normal mode, it didn't work and crashed (CTD) as expected. I retested a lot to be sure this time and to reduce all the confusion this might have caused here is the current standpoint.
1. I can start Radeon Pro before and after the game starts, both works fine.
2. I can start RTST before and after the game starts, in legacy mode, it is in both ways affected by Radeon Pro. It also does not matter if I start it before or after Radeon Pro.
3. RTST (normal mode) still crashes with any combination of Radeon pro, it does not matter which is started first, also elevated permissions do not change this. I still hope that the normal hook is not affected by radeon pro's settings, if only I could get it to work without CTD.
4. I can still use the normal mode of RTST with Radeon Pro if I deactivate all features who require API monitoring. Besides these features being very helpful they are also the features who make the legacy-mode overlay of RTST not work properly (blurry etc)...
This means I either use legacy-mode RTST + deactivating most radeon pro enhanced features manually, who make the overlay unusable or I use normal-mode RTST + deactivated API monitoring in radeon pro which automatically deactivates all enhanced features