From the art portal rules :
https://www.newgrounds.com/wiki/help-information/terms-of-use/art-guidelines
"We prefer to keep the spotlight on hand-made work"
"Do not submit images made from other people's assets or from scene creator programs"
So game screenshots are not allowed, like photography (aside from photography of sculptures, painting, other "hand-made works".)
That being said, you totally can upload these screenshots in your newsposts blog! :)
BaconflakesGD
Dang. I hope you can find a solution! :3
OofYeet1000
I hope so too... :3