Once I thought about some more I realized I could do integer scaling with DxWnd even if DxWnd didn't want to do it by itself. There's always the Windows Magnification API, so I used a small ahk script:

1DllCall("LoadLibrary", "str", "magnification.dll")
2DllCall("magnification.dll\MagInitialize")		
3Loop
4{
5WinGetPos,X,Y,W,H,ahk_exe WoW_patched.exe
6if (W = 640)
7	Magnify(3)
8if (W = 1280)
9	Magnify(2)
10}
11
12Magnify(MagnificationFactor)
13{
14XScale := A_ScreenWidth * (1.0 - (1.0 / magnificationFactor)) / 2.0 , YScale := A_ScreenHeight * (1.0 - (1.0 / magnificationFactor)) / 2.0
15DllCall("magnification.dll\MagSetFullscreenTransform",Float,magnificationFactor,Int,XScale,Int,YScale + 15)
16}

To make it automatically switch between zoom factors depending on the size of the game window (the game switching resolution). Then set DxWnd to "Suppress Release on backbuffer" which is apparently the fix for resolution changes causing crashes in DxWnd and I have the game integer scaled, with support screens properly scaled to fullscreen too:
https://www.youtube.com/watch?v=0XR60uOnp9Y

Assuming it's stable (I plan to play through the martian campaign soon) then this works perfectly so I don't need dgVoodoo for scaling, still would like to see it fixed though.

After testing some more, still not stable, so disabling resolution switching is still the way to go 🙁. Still remembering to use magnification I can at least get integer scaling.

I can reproduce the problem.
The game renders the entire map into an offscreen bitmap which is later blitted to the screen. So, it's weird why it does not update the counter. It doesn't do that even if I move the map behind the tooltip by the arrow keys to force the area of/around the tooltip be updated.
I think it's not a direct rendering problem but some other, like dgVoodoo causing some game timer not to run or sg like that (but I don't have the slighest clue how could it do that).

The resolution setting however works for me: at least two enumerated resolutions are needed (for the game to calculate resolution-slider positions) to avoid a crash at entering the display options menu.
When I set it to other than 640x480 and then enter a mission, it switches resolution and works without a problem.

Dege wrote on 2020-04-17, 16:53:

I can reproduce the problem.
The game renders the entire map into an offscreen bitmap which is later blitted to the screen. So, it's weird why it does not update the counter. It doesn't do that even if I move the map behind the tooltip by the arrow keys to force the area of/around the tooltip be updated.
I think it's not a direct rendering problem but some other, like dgVoodoo causing some game timer not to run or sg like that (but I don't have the slighest clue how could it do that).

Told you it was weird.

I actually got it working somehow, by disabling "BLIT instead of FLIP" (HKLM\SOFTWARE\WOW6432Node\Rage\Jeff Wayne's 'The War Of The Worlds'\1.00.000\Screen) and using an external framerate limiter to limit framerate to 30. But neither should be neccessary.

I don't suppose that helps you any way?

Dege wrote on 2020-04-17, 16:53:

The resolution setting however works for me: at least two enumerated resolutions are needed (for the game to calculate resolution-slider positions) to avoid a crash at entering the display options menu.
When I set it to other than 640x480 and then enter a mission, it switches resolution and works without a problem.

I should've said that I didn't want you to look into that. It happens like 1% of the time, so you'll need to spam going into/from support screens to reproduce it. And it might be because of something wrong on my side.