Can we run games from GOG.com in Virtual Machines, notably Virtualbox, VMware, and so on?

Depends on the game. GOG games are not special, they are not different from CD versions / Steam / Epic / Origin / Uplay or whatever else comes to your mind. The only real difference to Epic & Co. is that they don't require verification from a game launcher.

All DOS Games run in a virtual machine anyway (DOSBox), the games using ScummVM, run in ... well, ScummVM (which is not a VM, but a game engine that interprets the game scripts of many classic adventures and exists for different operating systems).

A lot of 2D games will run just fin in virtual machines, maybe with a bit of lag, but they run.

You will have problems however when it comes to Windows games requiring access to your sound and graphics accelerators, that depends on your used VM. If it allows passthrough or if it has a good emulation, it might even work.

There are exceptions, of course, in regards to some ScummVM packaged games not including the .exe file. With said games, you'd need the .exe file to run them properly through a different VM.

I'm not sure of the state of VirtualBox as of late. I remember there was an experimental 3D functionality to take advantage of video hardware but using it was.... off...

However if it doesn't use Direct3D or whatnot and it's all software, i don't see why not. Though depending on the version of Windows you may have to limit the Ram and CPU power it pushes to it. Win95 for example doesn't like over 80Mb Ram and 300Mhz. Though how it handles scheduling i'm not sure.

Though that will be likely with original software installs; Don't expect any GoG installers to work on it; Though if you extracted say DosBox files i'm sure it would run once the game files are copied (and not DosBox). So probably have plenty of ISO's on hand, or directly link to a CD/DVD drive.

I suppose if you had some of the first versions of the installers it might work... I did install stuff on XP a while back.

I think you'd want to use a virtual machine that supports GPU passthru.

I even downgrade VirtualBox to run 3d games in Windows XP VMs there

Besides what's been told already, there's also which system you'll be running your games on, and if your VM player can reproduce all its functions. As a notable example, from my tests, it's a PITA to get any VMs working properly with 3D acceleration.

This, I've done it on a Linux vm recently for work and it is so so in terms of difficulty (you can definitely google stuff up and figure it out). It was a Linux vm though. I've never attempted gpu passthrough on a Windows vm.

For personal use, originally, I got an external gpu and I was trying to get a gpu passthrough with that, but just setting up a egpu in Linux at the time was such a pain in the neck that I didn't go further.

Instead, I built a Windows box around the egpu I got that was just sitting around collecting dust.

Well i was referring to trying a 3D game and the humanoid models on screen were like 3 inches off from where they should have been, incomplete polygons, not textured right, etc. Like an early beta of a game where they got some values wrong for a playstation game or something.