Based on Retra's earlier comments, the answer to "if not, why not?" is pretty simple -- two photons are not in the same frame of reference because neither photon is in any frame of reference, and therefore there is no frame of reference which both photons are in.

If you were willing to assume that one photon did belong to a frame of reference, you would see that that photon was moving at 0 (impossible, but necessary for it to be part of the frame of reference) and all other photons were moving at c (since the velocity of a photon is c in any inertial frame of reference). Thus, all other photons would not be part of the same frame of reference as the reference photon; no two photons can belong to the same frame of reference.