Does macOS treat input from voice dictation the same as it would from a keyboard?
The short answer to your question is it's complicated...

Depending on how the application was developed it might use any number of different APIs from Swift, Cocoa, Carbon.

If your application uses Apple's standard user interface elements like text fields, then it likely has a way to put the text directly into the field, however Apple has probably added functionality to support other software by simulating keypresses.

How well this is supported depends on the application developer.

As an example an application like Citrix likely doesn't use any standard UI elements because it's got no text box to type into, instead it shows an image of a computer and records where you click on that image, sending that to the other computer, similarly it has to record your key presses, but evidently it's not doing that very well.

Microsoft Word is likely a very old code base that has grown from the days of Carbon which may explain why it's not working as expected, and I don't know what gVIM but I think you mean MacVim but as it's a port from another project it may not have been tested for this properly / it's not on their list of priorities.

For what it's worth I have had similar issues using software like TextExpander and Dash which auto complete sentences in Terminal, and using Apple's own remote desktop software like Citrix, so I think this is to be expected.