Legally you can make the video however you want. The type of video you make should depend on the viewbase you have. If they like spoiler free, do spoiler free. If they like full Lets Plays, do that.
We can't limit what you show in your videos and you don't need our permission. If you're wanting to just be nice and ask anyways, most developers have a Twitter listed on their profile.
----
In honesty, I doubt many developers even check Itchio weekly, so even if a DM system was implemented, you might not hear from them for awhile whereas just sending them a tweet will be much quicker. I myself only check Itch so often because my primary project is an asset that integrates Itch App and Unity haha.