If you put the stabilizing medium in the middle of the blank, without sealing it, and draw a vacuum, the stabilizing medium will just run up into the vacuum tube, especially with the way he does it.
One of the problems with unstabilized wood, at least in my limited experience and with respect to wood that actually NEEDS to be stabilized, is that it is very soft, even when drilling. I'd prefer that it be stabilized before the drilling process, if possible. However, if that isn't possible, you could cut and pre-drill the blanks, then put them in a baggie and try to suck the air out of the baggie. Of course, you're still going to draw some of the stabilizing medium out of the bag (or at least, if you're as clumsy as me you will), but you could put a trap in the line to help protect your pump. Any way, that would give you some penetration from both sides, and most especially from the inside near the tube. However, unlike when we fill these voids with a sanding slurry and CA or the like, the voids here will be filled with the (presumably) clear stabilizing medium, which means that you COULD have a crack/void/etc. that shows through to the brass tube once the piece is turned, and which you can't go back and fill it later. So, there are pro's and con's to it, from my perspective.