No. Assassin's Creed: Brotherhood is a standalone sequel. You can start it without an AC2 save file—no imports, no bonuses, no locked content.
Assassin's Creed Revelations checked for AC2/Brotherhood saves for Altaïr armor. Brotherhood does not check for AC2 saves. No bonuses, no penalties.
Jump in directly if you want. You'll miss context, but the game explains essentials. For the full Ezio saga, play AC2 → Brotherhood → Revelations in order.