Pre-drilling is a good idea, esspecially for antler.
The positive pressure helps, but the vaccum is the most critical part, it actually sucks it into the fibers for a good fill.
There are many hardening agents out there.
I have used lots of stuff including epoxy for antler, Thompson's brick sealer is my main formula mixed with a pint of rotted wood hardener.
It works on wood, ivory,ect...
I know a guy who uses styrofoam peanuts liquified with acetone, it basically makes a slow curing super glue.