George R.R. Martin teased the potential connection of Fire & Blood to the Game of Thrones spinoffs in a post on his blog, and fans who were hoping for a solid answer one way or another were probably disappointed.
Game of Thrones is all about preventing spoilers from leaking, and we can bet that similar precautions will be taken for the spinoffs.
That said, if one or more of the spinoffs is indeed a prequel to Game of Thrones, it would make sense for it to at least draw on the material from Fire & Blood.
The spinoffs are still in early stages of development with the focus on producing an epic final season of Game of Thrones, and Martin would certainly be expected to keep any big secrets to himself.