In Mage, the book of Worlds covers this: Awakaned calls the Dreaming Maya, and it is categorized as a Zone. You can see it with Spirit 1/Mind 1. You can travel it with Mind 3. The rules state than ONLY dreamspeakers can travel without the help of the Fae (or other Dreamspaker). You can read the mechanichs on page 185 (but is bassically that).
Page 44 of the old Tradition Book: Dreamspeakers has a paragraph explaining that Dreakspekers call the Fae "The invisible folk". And those dreamspeakers that follow the path of the Changeling are called Nunnehi.
I have not seen any Wraith - Changelling interaction (I have not read much on Wraith anyway, so big suprise here...). But my best guess will be Sandmen's Guild and their Phantasm Arcanoi, as it is dream related.
As you said, Tremere (or any blood magic practitioner) should be able to device a ritual if they have enough knowledge of the Fae. On other note, Kiasyd clan (from storyteller hand book of sabbat) are related to the Fae. Their discipline, Mytherceria, allows them to see the Fae, at level one.
Auspex 5 lets you Astral proyect. That is technically the way to reach the Dreaming.
The old Dark Ages book, talks about the Fae on page 261. In order to see through Glamour you must have Auspex (you roll Auspex diff 8). They even have a very funny table of the side effects of drinking Fae blood. One of the effects is to see through Glamour for a time.
That reminds me that Malkavians have something-something related to the Fae (like Malkav (THE Malkav) was of the Fae or something). Clanbook Malkavian talks about how thre Fae left for Arcadia but anything said in both clanbooks (the old and the revised) are usually followed by "but this is Malkavians speaking, so who knows if it is true?" kind of assertion, as expected from the clan.
I believe you will find similar things in Werewolf (I do not own the books, so I cannot help you here), but I suggest you look around Tribebook Fianna, as they are the closest to the Fae. If there are fetishes that allow any interaction, Awakened could also potentilly use them (and create them!).
I believe descriptions are intentionally vague, as crossovers are discoraged. But, as usual, it depends on your Chronicle. An "extranger" or two make for nice and refreshing NPC, too much and you cross over Fantasy Kitchen Sink. But you may want that, so it is ok.