Yes, you can send reinforcements to allies while shielded. You can also activate a Shield of Peace while your reinforcements are on their way to an ally.
However, you will not score any points in the Clash for the Throne if your ally uses your troops in battles against other players during this event.
Other than that, here are a couple more tips:
- You cannot activate a Shield of Peace when you have reinforcements in your City.
- You cannot send reinforcements to a player who is protected by a Shield of Peace.