Yes, of course it is.In fact I have lifelong experience with shellac. My father was fine art cabinet maker, and as a little kid one of the jobs I used to get given was using button shellac to fill tiny imperfections in cabinet work. You melt the shellac over a candle, smear it into the hole, and then the surface gets refinished.
Button shellac is probably the most favoured traditional adhesive for use on Javanese wrongkos, however, it is not a very strong adhesive, and only works well when the gandar is supported by a pendok.
Shellac is sometimes used in recent times as a filler for silver handles in Indonesia, but its not very durable, and over time it will crack, and you can hear the pieces rattling around inside the handle.
The traditional filler for sword and dagger handles was damar mixed with beeswax and a solid filling agent. This stuff sets like rock and will never crack, but a handle can be fairly easily removed from a blade simply by heating the blade.
In all the mandau that I have had to restore, the lump on the bottom of mandau handle has displayed the properties of damar + beeswax, and sometimes with a filler, like the Javanese handle filler. When I have had to replace this lump, I've always used damar + beeswax + plus a terracotta filler.
I don't know the tree that damar comes from, but when you melt it, it has a very strong pine-like smell, and is very flammable, in fact, its pretty dangerous stuff to use.If you get a drop on your skin it just sticks and burns right through. Pretty painful.
http://www.rfpaints.com/PUWin/Damar.htm