Short answer: no.

“What with being a knight and allies with King Arthur and Merlin and all...”

What continuity are you talking about? You provided the link to New Earth but wrote the above which doesn’t describe NE Blood at all.

I'm not saying the specific Earth type. I'm sayin-.... It's the tag, isn't it?

Sorry. I'm only asking if Jason Blood could be a fable or not. That's all

A fable is only a thing in the continuity of Fables, which is a Vertigo series with several spin-offs. It is not, in any way, relatd to any mainstream universe and has never crossed over with it. "Fable" is not a thing in any universe where Etrigan exists.