Not all of them. Garmin car units yes (at least some/most of them), TomToms on the other hand are unusable as it's not possible to tell them to stop sticking to roads, even though you can enter coordinates into some of them. I don't know what's possible with Navigon units.
Of some interest - the newer TomTom units (firmware 9.XXX) will produce a real set of coordinates on the satellite page. The older ones (firmware prior to 9.XXX) will produce the road-snapped coordinates. You cannot enter coordinates on any of the following TomTom models that employ their EasyMenu system: Ease (Start2 in Europe), XL335SE, XL335LE, XL335LM, XL350, XL350T, XL350M, XL350TM, (XL IQRoutes2 in Europe), XXL550, XXL550T, XXL550M and XXL550TM.