Solution 1:

The blog post introducing Greed Mode lists all possible locations for Super Secret Rooms in Greed Mode:

  • above the Shop
  • to the right of the Treasure Rooms
  • to the left of the Cursed and Devil room
  • below the exit room

enter image description here

It doesn't mention normal Secret Rooms, so I think there are none in Greed Mode.

Solution 2:

I created an account just to add my input as well. I can't comment on Powerlord's post but I also found a secret room. Mine was above the curse room and left of the shop. The only issue is that it was blocked by the cement wall blocks (similar to those around the black hearts in levels).

So unless you're flying and have a bomb handy I don't think that had a potential for entry. I found it with the Spelunker's Hat.

Also if you find a counterfeit penny in greed mode... You pretty much win.

Solution 3:

I finally bought the X-Ray Vision item, and it has never revealed and opened any Secret Room on any floor.

EDIT:

I also tried with the Blue Map (which shows Secret and Super Secret Room locations on the map) and I haven't found one.

If there are Super Secret Rooms in this mode they are very very rare.

EDIT2:

I've found a couple of Super Secret Room in my last run (having X-Ray Vision):

  • on the left of the Silver Treasure Room
  • under the Exit Room

So you can find them occasionally.