A guru in a dream typically represents guidance, but the wisdom offered usually comes from inside you rather than any external authority. Their presence can point to a decision you already sense the answer to, even if you haven't admitted it yet. Listening closely to what a dream-guru says is often just a way of finally listening to your own inner knowing.
If the ascendant sign is not from the same nature of the request or the requester, the invocation would be meaningless and; the requester bewares! - Picatrix (Andalusia, ~1000.AD)