They can have a normal looking belly and still be het pied. I used to have a pair of het pieds that did NOT have the markers, I did produce pieds with them so they were obviously hets. However the interesting thing was that many of their babies that were 66% het pieds DID have the markers even though the parents did not.
Also since what are called 'the markers' are heavy solid black lines down the sides of the belly, I doubt that they would be obvious in an albino, but it would be interesting to see if you could tell.