I have no idea if Nvidia accounts for ReShade use in their drivers, the last Nvidia card I had was a 6600GT, I seriously doubt AMD accounts for it though as unlike their competitor they don't have an army of employees.
In my experience if the ReShade games compatibility list says ReShade works with a game then it works with a game and all of their shaders are hardware agnostic meaning that as long as your GPU supports at least DX9 (when programmable shaders really became a thing in spite of Nvidia introducing them in their Geforce 3 line) you're golden when it comes to them working.
DGVoodoo is meant for GLide games and games that use DX8 or less although ReShade provide a DX8 to DX9 wrapper themselves that usually works ok, DGVoodoo's support for games based on DX8 and DX9 is a little sketchy and most DX9 games work fine in modern hardware/software environments anyway.
As for OpenGL games it depends which version of OpenGL said game uses, really old (1990's) OpenGL games sometimes work and sometimes don't, for the ones that don't QindieGL or GLDirect wrappers sort them out but for later games using OpenGL 2.0 or higher you just have to hope that the developers didn't use too many proprietary Nvidia OpenGL extensions because they will never behave on AMD hardware because AMD can't execute those extensions even if the hardware is capable (which it is).
Some OpenGL things like the Polymer renderer in EDuke32 won't behave on AMD hardware and their developers claim AMD driver bugs are responsible, this usually means they deliberately or unknowingly used proprietary Nvidia code, not that AMD driver bugs don't exist for OpenGL, they do, they're just not usually responsible for the disastrous performance these apps experience.
ReShade MXAO does not work on DX9. Using dgVooDoo does not help. I tested it today with NFS Most Wanted. Also, I tested with AC Odyssey that the MXAO feature is working very good on DX11. I also saw that ReShade errors were included in the nVidia fix list. I think features like HBAO and HDAO come with DX11. So the answer to the topic owner is "NO". There is no ambient occlusion feature for DX9 and earlier. Force cannot be used. The "game" developer can only enable this feature by switching to DX11.
MXAO works fine in DX9 provided the game uses an accessible depth buffer (without the depth buffer the shader cannot tell how far apart objects on screen are and as such cannot apply appropriate shading).
I don't know why it wouldn't work with NFS Most Wanted but for F.E.A.R you have to disable soft shadows and anti aliasing in game to be able to access the depth buffer.
Also worth noting some DX9 games have the depth buffer reversed, vertically flipped or horizontally flipped, all of which have to be accounted for in ReShade before effects like MXAO can function. For example Vampire The Masquerade: Bloodlines has a reversed depth buffer. look at the stairs here with a reversed depth buffer set up MXAO correctly applies shading.
Indeed, Vindictus does not allow access to its depth buffer, apparently because it's an online game and doing so would interfere with its hackshield.
It's just baffling that Nvidia's implementation of forced AO is able to bypass that (but no such solution exists for AMD).
From what i can read: "Ambient Occlusion: This setting can be used to force Ambient Occlusion (AO) in supported games." That feature can be enabled, or "forced" (if you want) only in "supported games", so, the game must support it. I think you didn't read that text carefully...
In case anyone's still following this, I have now successfully enabled AO in this game where it was supposedly only possible through Nvidia's control panel and impossible for Radeon owners.
This works by using a modified version of ReShade (made possible by it being open source) called ReShade Debbie. In it, the stock "online game" check for depth buffer access* is disabled, aka. it doesn't remove depth buffer access even if you're playing an online game.
It's taken some time tinkering with ReShade to get to work properly (as seems to typically be the case for ReShade AO), but it's worth it.
If you're new to ReShade or its AO, first of all, expect to dedicate some time to it. This video is a nice tutorial. In the right-most tab (titled DX9/10/11/Vulkan), I had to tick "Copy depth buffer before clear operations" and the "CLEAR 1" DB. I had to make sure to turn off in-game anti-aliasing and color correction (this second one was only possible via editing the game's config file). Your game may be different. You might have a changing DB list depending on in-game effects; I haven't yet figured out how to dynamically change ticked DBs with the changes.
*I think this has been implemented due to concerns that DB access would enable hacking, but Nvidia owners have already been accessing it for years, so it seems like excessive caution. Still, just to be safe, I won't link to it. Google and use at your own responsibility.
Passive-aggressive shout-out to all the naysayers who had convinced us we're out of luck :p