I don't think many (if any) team starts out with a plan to tank a whole season....it not only affects the team dynamics but the reputation/stats/potential future of all the players & coaches (btw...how could anyone be sure in this day and age one of them wouldn't rat out about it or use as a bargaining chip for more money or extortion against being fired??). Granted, not everyone would have to know but a few people (at least the head coach and maybe OC/DC) would need to be in on it and would then have the FO over a barrel when there was an eventual falling out.
HOWEVER...when a tipping point comes mid or late season and you are 3-8 or 4-9, etc. , I can see (and really would not have a problem with) a team caving and losing its remaining games to be in a better position come draft time. I'm sure that's happened and teams have taken that chance to be in a high draft spot vs. finishing 7-9 or 8-8 (alas...the Dolphins apparently have never got the memo/plan).