I'm inclined to take a somewhat opposing view, but that isn't just to be contrary.
By that I mean there is a "right" answer vs. a wrong answer in terms of Sponsored Magic and Hexing. Namely, the "right" answer is what works at your own gaming table.
Having said that, I do have my own thoughts on Hexing. Hexing basically breaks down into two types, these are deliberate Hexing and accidental Hexing. Any type of magic can/should be able to deliberately Hex something. The accidental Hexing should really be limited to mortal magic, and possibly Hellfire Sponsored Magic.
There have been a few instances so far in the novels and short stories where one type or another of non-mortal magic was used to deliberately disrupt technology. There has also been a few very clear examples where non-mortals who had potent magic didn't suffer the ill-effects of accidental Hexing that occurs to Harry.
In Last Call for instances,
a "woman" uses a credit card to purchase somethings at a cheap magic/variety shop in Chicago. That confirms to Harry to whatever the "woman" was, she/it wasn't mortal since the magnetic strip in Harry's credit cards never function for more than a few hours, so he doesn't bother with them. The "woman" on the other hand, didn't encounter any sort of problem like that.
That sort of thing does make me think that a mortal instrument of sponsored magic isn't going to suffer from accidentally Hexing things, unless doing so fits within the Agenda of the Sponsor. Hence my inclination to have that applicable to Hellfire, since that is about chaos/disruption/destruction and also not being very nice to anyone, including those who wield Hellfire... Now if the person with Sponsored Magic was also a practioner (or had Mana Static), then they could still accidentally Hex things, but that would be because of something innate to them, and not because of a Sponsor.
-Cheers