From the wiki:
New Secret rooms: Every single level contains one standard secret room (Marked with a white question mark) and one new secret room (Marked with a grey question mark). The new secret room is almost always only connected to exactly one other room, with the only exception being when it is also adjacent to the regular secret room. The standard secret room still can be located using the three adjacent rooms principle, but if the new secret room is adjacent to the regular secret room it counts as one of the three sides. Items or tarot cards which reveal the regular secret room on the map do not reveal the new secret room, though X-Ray glasses will reveal both.
So yes, there's one of these new rooms on every floor. They're hard to find, since they're not surrounded by other rooms like the other, and also make the old secret rooms harder to find, since they can count as the third room surrounding the other.
I happened to find the Spelunker hat just once since the DLC came out, and it failed to find the new room; be aware anyway that there are still many buggy items, and this may be the case, since it failed to find the normal secret room too.