The absorbed veins will be completely absent; they will have receded and you should see very little blood, if any at all. The veins won't dry out, per-say, but the membrane can. Your application of oil will help with the moisture there, and leaving the duckling to do its thing with the incubator lid on will keep moisture in too.
The most important thing is for those veins to recede before you proceed further with an assisted hatch as those indicate that the duckling is still physically linked with the membrane and will bleed out through those veins if they are broken. It will also not have absorbed the yolk until after the veins have receded, if not later still.