First, it solely depends on the way he wires the subs.
The actual placement of one driver in the "back" of the enclosure makes no difference at all. May as well "slide" it to the front baffle if it makes it easier to imagine the system.
Okay now you have two drivers in a box, one's inverted, no big deal. If you also "invert" the wiring, that is make it out of phase, it would just be a typical sealed, two subwoofer box. Sure one of the subs would be mounted backwards, but it would also be working reversed, so it would sound just like a normal 2 driver box.
However, if the intention is to run it isobaric, then there are several HUGE problems with that design. The idea here is to run two subwoofers together, that is in phase with each other in order to cut box volume in half. You spend twice as much money on 2 subs, and need twice as big an amp to run 2 subs, and you only get the same output as 1 sub in a larger box. So the comment that isobaric loading is for people with too much money, well, thats partly true. More often than not its for people with not enough space for a big enclosure though.
The problem with that design is that you need the drivers very very close to each other to "couple" acoustically. Generally you face them towards each other and run one out of phase, with just enough space between them that they don't touch, and thats it. In this design there is an entire volume of air in between that will result in the "back" driver not coupling with the front and their produced sound waves most likely canceling each other out.
Back to the drawing board.