Certainly there are locums rad oncs out there that are worse than NPs.
Yes, it theoretically may be possible in PP to train an NP to be a fully independent rad onc over a period of many years (I have never seen or heard of it done, but I suppose it's possible).
But an NP should not be covering a rad onc clinic for a week at a time alone, The NP is going to staff simulations, check images, make decisions about whether to hold or re-plan treatments, do emergent sim and treats, start new patients, approve SBRT, electron set ups, deal with any dosimetry issues that come up (hey, this boost wasn't approved yet and there is only a GTV drawn yet, can you make a PTV and approve it, etc). You know, things any minimally competent rad onc who completed residency should be able to do. In reality, physics and dosi will make the decisions and the NP will just nod, the same way they do for incompetent octogenarian locums.
Are you serious?
If you are talking about having an NP on site to deal with patient issues and having a rad onc available remotely for general supervision, that's one thing (and I agree that concern over this is way overblown -- no issues to let rad onc cover Friday remotely and be available by phone if needed), but what we're talking about here is the NP is flying solo and the rad onc is scuba diving in Australia. That was the hospital's plan.