Hmm this is a tough one, I think it's fine for the definition of 2D to be stretched a lot, but it is still a 2D game jam. I think 2.5D is okay and anything that's still in the spirit of a 2D game, but I think the Mr Hopps example is ultimately a full 3D game so it would lean outside of that. With the Mr Hopps example, maybe if that was a point and click game it would be a bit more on the line(Although even then it's a bit murky), but if you are walking around a 3D environment, it would be hard to call it 2D.
Hopefully your idea can work within that in some way, I appreciate your participation!