1. In my opinion, yes, providing it is water activated gum,
with self adhesives, it is often wise to leave the stamp on the paper
and cut around the stamp.
Caveat: one has to be vigilant that the stamp is not printed
with water activated ink (fugitive ink) always check.
Largest offender Netherlands Indies. QV India revenues.
2. For stamps stuck together, there is one mantra, one has to chant
"patience", "patience"

Many a beautiful mint stamp has been ruined by trying to seperate
before time, or removing a recently applied hinge on used.
To seperate stamps, it can be fun to construct your own "sweat box"
(removes hinges as well)
http://stampcollectingforbeginners....eat-box.html