Yes, you will see them with the wheels off. They are held in place with a single allen bolt. The only time I cleaned any they were covered in metallic swarf (goodness knows where from!) which stuck to the magnet so it was a case of gently wiping them and pulling it off with the fingers.
You may find that on the rear there is one sensor at the front of the diff instead of at the wheels.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)