I believe that's correct. Also, as far as getting the effect of the 2 RB's for a given team, I suppose you can do it one of two ways.
1) Take human control of all teams at the beginning of the season and in week 1, go into the substitutions screen for the team you want to have a 2 back rotation. Stick the given back in the given formation that would make the most sense. Unfortunately, there is no individual set substitution screen before you go into a game.
2) Change the stamina using Finn's editor to something considerable mediocre for each of the 2 backs so that they will rotate in and out. The drawback to this is if one of those given backs is traded during the year and you want your roster to reflect the trades as they happen, you will have a lower stamina back on another team. But, as long as depth charts are accuracte that may still work.