If I knew that all the Cardinal players allocated were on one of the NFLE teams, I'd have made sure to follow that team throughout the NFLE season. (Even a cave man could TIVO it in advance).
But, even though I jot down at the beginning of each season which Cardinal players were with what team, I'd forget - all the German teams (Rein, Frankfort, Hamburg, Hot Dog etc.) tended to blur in my mind and I'd forget which was which. For example, as of this moment, I have no idea who Greg Lee played for (if he wound up playing at all).
I'd guess the main reason why a minor league setup would be tough to execute would be the injury bugaboo characteristic of a collision sport like football.
It might be interesting to replace the rookie minicamps with a month's worth of 4 minor league rookie games; but my sense is that most coaches would prefer to use these minicamps to indoctrinate their rookies into their team's nomenclature, system and culture.