To my understanding one of the main reasons the Bulgars didn't convert to orthodoxy sooner was because they didn't want to look subservient to the emperor, now if I'm not mistaken the caliph downright demanded subservients as part of conversation, so If anything wouldn't this more than anything secure bulgar orthodoxy?
And I don't see the caliphate having the same kind of Balkan success as the ottomans did, they might even ultimately get kicked out of Europe depending on how quickly they come to fight the bulgars and if the bulgars are Christian at that point the city's population could be a security risk for the caliphate.
And I don't see the caliphate having the same kind of Balkan success as the ottomans did, they might even ultimately get kicked out of Europe depending on how quickly they come to fight the bulgars and if the bulgars are Christian at that point the city's population could be a security risk for the caliphate.