First off, obviously a god can, but who else can?
The recent player companion "Blood of the Coven" suggests that Witch Patrons can take many different forms, including highly ranked agathions, angels, archons, demons, daemons, and devils, aeons, kytons, owbs, and nightshades; fey lords, nature spirits, and ancient denizens of the first world; but also the collective unconsciousness of "mortal desire and purpose given direction by the beliefs of countless minds and hearts." Now a patron is really more akin to a teacher than someone who actually gives you power that you didn't already have access to, but I admit something really abstract like "the collective unconsciousness of mortal desire" doesn't seem like anything that would put together a lesson plan.
Certainly one does not need to go through a deity in order to access divine magic- druids cast divine spells just fine and "the Green Faith" venerates things more fundamental than gods. Indeed it seems like the Domains that deities grant to their clerics are themselves more fundamental than the gods- Curchanus has the Beast and Travel Domains, the former was stolen by Lamashtu and the latter given to Desna. A lot of domains are things that the gods themselves experience (e.g. Travel, Madness, Glory) or embody (e.g. Strength, Protection, Magic) rather than things that spring forth from one or more deity with that domain in that portfolio. Some of the mysteries that oracles have appear to be even more fundamental than that. For example every deity experiences Time (or at least causality)- Cayden was not a god and then he was, Aroden was alive and then he wasn't, Asmodeus was not the patron of Chelia and then he was, there were no undead as nobody escaped Pharasma until somebody did and then there were, Desna did not have the Travel domain and then she did, etc.
So can you have an oracle that's cursed/empowered by "time itself" in the same sort of way that a druid may be empowered by "nature itself"? Is all that is needed for an oracle to come into their power to have their eyes opened to their mystery and then they can access divine power that's just lying around? Can high ranking outsiders who are themselves not gods or demigods make oracles? Do oracles sometimes just happen purely by accident and there was no intention behind their curse at all?