Reception Bonuses only apply to Receptions made by players of the Positions designated. The Player making the reception will receive a Bonus based on his Primary Position.
If a Player is designated RB/WR, he will be given the Reception Bonus for RB, not WR, and not stacked/both.
*Note that all of these will stack with a standard Reception, if any Points are given to the Standard Stat Category (ie. PPR/Half-PPR)