It can enter raid of the BLU level range. 4.5 he will be able to do BCoB and Crystal tower if he have a party for it.

He won't be able to enter any omega raid nor the future one before he get his level decap and hit the said level.

They said many of the blue spell are just completely unbalanced and unfair, the raid boss will more likely get his ass handed to himself even in synch' party if a BLU is part of the dance.