Many do use their own non-canon fanfic as canon, yeah. Especially "shippers". (Folks who "ship" -- as in relationSHIP -- various characters. Like, say, imagining that Obi Wan was Anakin's gay lover.) For those, yes, you are correct.
And yes, that includes a disturbing majority of Jesus fanboys' head-canon. Especially those who haven't even read the source material. (Which seems to be most Christians, sad to say.)
I tend to be the of the Old Star Wars Testament idea that if it doesn't happen in a canon work, it doesn't matter, and you can't appeal to fan-fic to override canon.
(Mind you, I'm NOT using "fanfic" as a derogatory term. There are some great fanfic stories out there. Professional author quality. Just saying that if it ain't canon, it ain't canon, and that's that.)