Based upon your PS3 experience (and my 360 experience with porting NCAA rosters), I would expect that it is possible to port earlier Madden 360 rosters to later versions of Madden. No matter what approach is taken to transfer data, the key to success is to understand the structure of the Roster in the version of the game to which you wish to port data. Care must be taken to not alter the structure of the destination roster. Any data from the origin roster which does not fit the structure of the destination roster (such as the Canton Teams referred to above) must not be moved over.
Probably the most efficient method for porting data would be to use one of the Editors to Export the data from both rosters into "*.csv" files, then use the "Copy/Paste Values" capabilities of Excel to move selected data from the origin roster to the destination roster. When finished with the porting activity, use the Editor to Import the modified roster back into a game format.