Q: I'm wondering how religions might react to this?
Religions usually do away with competition, they will deny the new Maguses actually having any powers, or being new prophets. They will frame the Maguses as an impostors, or magicians. When the magic cannot be denied, these people will be regarded as posessed by demons.
Q: Would some say that what they do is miracles while others arr demonic?
Depends on where the magic happens and how it affects the religion's believers. When the magic can be directed, selling beneficiary magic activities as Pious and Rightious, a religion may embrace the new Maguses. A religion that does not have any tolerance however will always attribute the magic to the devil.. When beneficiary, priests will say the improvements are a deception or illusion. The Apocalypse is near..
Q: Would they hunt or persecute any magic users regardless of if they're aligned with them or not?
They always did that.. when they were in the position to do hunting and persecution..
Q: Would we see a global schism as religions fought internally over what to do?
Absolutely, believers will fight over whether they should condemn these people. Maguses pose a risk for religions. One really strong Magus can gain followers and split a religion like the Christian church. Be regarded as a false prophet by one church, acknowledged as a prophet by another church, of the same religion. And common views regarding a Magus can change in history, without splitting the religion. This actually happened to Merlin, who was regarded as a (son of a) demon in early sources, and 500 years later deified as a hero, by the Plantagenet dynasty.