The Dreamer will have in it's data all evil roles in current match, unless if there is only 1 evil for corrupted or evil disguised.
When using the Dreamer ability on a card, the Dreamer will tell you which evil that card could be, not is but could be.
Truth Example: Baa card is seen as Baa to Dreamer.
Corrupted or Evil Example: Baa card is seen as Minion to Dreamer.
However; the could be mechanic is due to if you use it on a villager or outcast, the Dreamer will still tell you a evil role that could be that card, but that doesn't mean that card is that evil role; it only is if it is a evil role.
Is this understandable enough?