Yes, you can participate in multiple Raids at the same time as long as your alliance has enough Keys to launch another Raid in addition to the one that is already active.
Note that raid energy consumption is the same across similar raid types. If your alliance launched 2 Ultimus/Doom Raids, the same Ultimus Energy is shared between these Raids. Spend them wisely!
Note that raid energy consumption is the same across similar raid types. If your alliance launched 2 Ultimus/Doom Raids, the same Ultimus Energy is shared between these Raids. Spend them wisely!