Does a source of photon emission "sense" if the photon is absorbed? Can the absorption of a photon be 'felt' by the source that emitted it? At least, if we assume that it emits a steady stream of photons? Is there a back reaction of some kind on the source?
 A: This sounds like the "retrocausation" in the Wheeler–Feynman absorber theory. Since the only invariant quantity in relativity is the relativistic interval, which is zero along light like curves, all "place-instants" of photon's existence are technically not separated from each other in the (pseudo) metric, and hence causal, sense. This means that photon emitted by a distant star and photon absorbed by your eye are spatio-temporally "co-located" in the relativistivc spacetime. In other words, nothing prevents the emitter from "knowing" or "feeling" that what it emitted is "eventually" absorbed. One does not have to adopt such interpretation however, and it is of a more historical interest.
Koberlein's blog explains:

What Feynman showed was that despite it’s oddness, the requirement that emitted light be absorbed doesn’t violate causality. It came to be known as Wheeler–Feynman absorber theory (John Wheeler was Feynman’s advisor). There were some problems with the model, however. In particular Feynman assumed that charges couldn’t self-interact. In other words, an electron couldn’t emit a photon only to reabsorb it later. Of course there’s no real reason why that should be forbidden, but if you allow it in the theory you get a divergence of interactions and the model breaks down. This led Feynman to abandon the model eventually, but it was deeply influential in his development of quantum electrodynamics, for which he was awarded the Nobel prize.

Here is the original paper: 
Wheeler, J. A.; Feynman, R. P. Interaction with the Absorber as the Mechanism of Radiation. Reviews of Modern Physics 17 (1945) no. 2–3, pp. 157–161 
A: It is clearly acausal that for a photon to be emitted it must be absorbed. That's action at a distance. That is not what time symmetry means. That view is known to not be correct, and there are no problems with advanced and retarded potentials, it is known what they mean and how to deal with them, and it is not this. Wheeler and Feynmans paper is clearly just off, and maybe of historical interest but no longer useful or valid  scientifically. Feynman abandoned it. Plus we know that plenty emitted photons are still traveling outwards in the cosmological spacetime of the universe, so does that mean we didn't emit them? 
The Wheeler Feynman interpretation breaks causality, and is not mainstream physics nowadays, it's been known to be off for years. 
