Can't see it mentioned anywhere on the page but the announcement video on GOG Classic Vault's youTube channel featured an employee holding up the case for the original PC version. So is this included and is the original DMC3 PC release included with the HD trilogy?

No, they don't include DMC4 Vanilla or the original PC port of DMC3.

According to the wiki there is actually a cheat code to revert the Special Edition changes so you can play as if it was the original pc version:

"No saved data must be present in order to activate the code, if there is any data, it must be deleted."
"On the title screen (where "Press Any Button" is displayed) type in "devilmaycry" using the keyboard to bring up the settings confirmation window."
"Likewise, in order to deactivate the original settings, the saved data must be deleted."

DEFINITELY let me know if this is fake.

(Still should have the original PC version as a bonus for different performance. Probably.)

Cheers Zaphero for the response! Sounds very interesting...
Unfortunately I'm not going to consider buying this until GOG fix the technical issues left unaddressed for over two months now. This being part of the Preservation Program is frankly a joke.