To be fair he has a point, if training civilian is important for you then dont even consider HPSP, look into FAP or direct commission after youre board certified if you really want to serve. If its about the money then just take out loans, in the long run its not worth it financially if you go into anything other than primary care.
That being said the AF had 16 inservice training spots and 13 civillian deferred, so probably the better odds of training civilian (though I have no idea what the numbers are for the other branches). From what Ive been told 8 of them are active duty residents at civilian institutions (the 6 at WP and the 2 at Nellis).
As far as what its like in the AF once youre practicing, again this is based on my limited knowledge in speaking with AF EM docs, its very few high acuity/high volume EDs but a lot of over glorified Urgent Care centers. I lived by one of these and anything remotely serious, even if on base, would get rerouted to the civilian hospital a few miles away. Many, if not all, of the docs worked at local civilian EDs to actually see anything.