Of course you can. But you will need to learn a lot about DOS, DOSBox, the config files, how you load games with config files...

A lot to learn for something that already works (GOG.com games ship with a copy of DOSBox for every game).

Each game sold on GOG comes with a copy of DOSBox that's been pre-configured to work with the game. Most of the time, the settings are optimal enough, but if you want to change any settings, just go to where the game is installed and edit the config files there.

And don't worry about the fact that sooner or later you'll have a dozen copies of DOSBox floating around your folders. DOSBox doesn't take up much space. ;)

If you want to run a GOG game in a separate copy of DOSBox, basically what you need to do is configure your copy of DOSBox with the best settings for the game and mount/imgmount the appropriate folders/files. There may also be additional things you have to do, which you can figure out by looking at the config files included with each game.

Dos games that GOG sells are being played through DOSBox. If it is a hybrid DOS/Windows game I have no clue 😉

If you know what to do you can easily play the dos games through DOSBox, you will need to install them nevertheless and THEN point dosbox at them to play.
There is no universal way though.

I could never make the Fallout demo work as playable in DOSBox so far but... I haven't been trying in the last 3 years

[EDIT]
Got it from GOG.com
Fallout 1,Fallout 2,Fallout Tactics Free for 48 hours on GoG
FREE fallout 1,2, & tactics