An interesting set of questions. A cell without a nucleus (a circulating RBC) cannot express any protein -- it has no machinery not only for decoding protein instructions, but also for making any proteins. As I said above, a red cell is just a cell membrane around a dollop of hemoglobin, the chemical used to transport oxygen around. There are no organelles, no components -- just hemoglobin. So no expressing spike protein.

Depending on how prepped, components other than RBCs are reduced to either zero or to such a low number that they are essentially not remarkable. Any free RNA spikes would have been in the fluid (plasma) in which the red cells are suspended, not in the cells themselves. The plasma will have been largely removed to pack the cells so little or any would be left. I suppose if the person were freshly infected/spikeshotted there might be a few spikes (or viral particles, for that matter, in there -- blood comes with all kinds of contaminants (other viruses as a case in point) that are not examined or cleared before administration).

This is why transfusions are nothing to do cavalierly, but in general if you are getting them you are really, really short of oxygen carrying capacity and you need them. Minor transfusion reactions are common because there is "lots of stuff" in any transfusion. A few (hepatitis, HIV) are screened for; most are not. However, having said that, most of the reactions are minor and the recipient's immune system and other cleansing mechanics clean up the transfused products well -- especially packed red cells. But it is not unusual (not common either) to pick up some viral disease that came from the donor.

So "purified" probably too strong a word. Other than glycosylating and freezing/thawing, packed cells will be "almost pure"...and biologically this is almost always good enough. As I noted above, if you are getting a transfusion, I doubt worrying about whether the person was vaccinated or not should be high on your list.