"In any case, the SEP is really just a conjecture. Also there is something fundamentally wrong with a theory in which the existence of radiation is frame dependent. Surely it should at least be possible to settle this question empirically?"
No, look at the Unruh effect.
Virtual photons in inertial frames are real photons in coincident noninertial frames. This is the origin of the firewall debate on black holes.There is a creative tension between equivalence principle and charges emitting photons
If a charge sits at surface of Earth it has a constant proper acceleration in a static LNIF. Feynman would say no problem  constant acceleration does not cause real photon emission  to who? others ask.
If you accumulate a lot of unbalanced electric charge and just let it sit on a lab table do you expect it to radiate real photons? Where is the energy coming from?
In WheelerFeynmanCramer  the emission of real photons is a transaction between emitter and absorber with advanced confirmation. So now there are four cases emitter rest frame in LIF or LNIF, absorber rest frame in LIF' or LNIF'
We do not expect any real photon emission in the geodesic LIF <—> geodesic LIF' case. What about the other three?

Unruh effect  Wikipedia, the free encyclopedia
The hypothetical Unruh effect (or sometimes Fulling–Davies–Unruh effect) is the prediction that an accelerating observer will observe blackbody radiation ...
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Hawking radiation  Wikipedia, the free encyclopedia
The Unruh effect and the Hawking effect both talk about field modes in the superficially stationary spacetime that change frequency relative to other coordinates ...
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On 6/29/2014 9:39 PM, Jack Sarfatti wrote:
Still up in the air
Sent from my iPad
On Jun 29, 2014, at 7:00 PM, Paul Zielinski <iksnileiz@gmail.com> wrote:
Here is a more in depth discussion of the problem by R. Scalise, which raises doubts about
Feynman's answer based on more recent work:
http://www.physics.smu.edu/scalise/P7312fa12/ChoiceCutsCh52.pdf
On 6/29/2014 6:47 PM, Paul Zielinski wrote:
Informative discussion on this topic by Kevin Brown available here:
http://www.mathpages.com/home/kmath528/kmath528.htm
On 6/29/2014 6:37 PM, Jack Sarfatti wrote:
1) an electric charge on a time like geodesic should not radiate transverse photons.
2) Feynman showed that a charge in uniform acceleration does not radiate.
This is obvious since radiation reaction depends on the jerk covariant derivative of
D^2V^u/ds^2
Note that this is complicated in LNIFs.
Sent from my iPad