The thing with theory is that it's an attempt to explain the music that we hear and love. In some instances, traditional interpretations don't provide the analysis we're looking for. In those cases, theorists/analysts typically try to find interpretations to describe what's happening, which often takes the form of drawing parallels between common/traditional concepts and what's actually happening in the music.
I recall going over this in a theory/analysis class in college, where the teacher had chose to interpret an unusual chord progression within the frame of an unrelated key. I challenged this but in the end, his interpretation was the best we could come up with. So even though it didn't exactly make sense in the standard approach to analysis, it was the only thing that really provided us with any sort of explanation that made sense.
So I can't say that Pollack's interpretation is exactly wrong but I don't really agree with it. It's in his wording, where he says, "used...as though" and "surrogate". If he said vi is the dominant, I'd argue he was explicitly wrong, as that, by definition, is not what the vi is. In trying to reconcile this, I'd try to listen to the piece a few times, paying attention to how the vi chord feels and where it seems to push/pull. If it feels like the vi prepares us for the V, it seems appropriate to say it acts as a subdominant. If it feels like it wants to resolve back to I, then we could say it's acting as a dominant. I don't believe I would feel that myself but you may and Pollack clearly did.
One thing to consider here is how/where/why you might be doing this analysis. If you were taking this sort of approach to analyzing a piece of music within an academic setting, then you would want to be a bit careful with how you make your argument and possibly bring it to your teacher prior to submitting it, particularly if it is an important assignment, like a final paper. If you're just looking to have a better understanding of a song to allow you to perform it better, or just appreciate it more when listening, then analyzing along these lines is just as valid as analyzing vi as submediant, or purple for that matter, because it's just about you at that point. If you're trying to work with a band to play this song (and everyone happens to be familiar enough with theory), you might confuse everyone or cause an argument about the validity of the analysis but you may also find that it brings everyone to a new interpretation that allows you all to play the piece better as a group, regardless of how "correct" your analysis may be.