Based on the companion dialogue after dreams, it's implied the dream visitor has at least a different appearance for each of them.
For example, Gale always refers to the dream visitor as female, even if Tav's is male, Karlach describes hers as a "golden paladin," etc.
This is contradicted by the ending of the game where you see that all four dream figures are the same person, or similar enough that the differences are very slight.
