Yes.
Change the first line of the following script to point to where Stencyl is installed, and then run it in the terminal. This sets up your Haxe environment to be (roughly) the same as Stencyl's for that terminal session.
DIR="/Applications/Stencyl"
DIR="$DIR/plaf"
# HAXEPATH contains haxe and haxelib executables
# HAXE_STD_PATH is the Haxe Standard Library
# HAXELIB_PATH contains installed haxelibs
# NEKO_INSTPATH and NEKOPATH both point to the Neko install
# HAXEPATH and /usr/local/bin (for neko) are added to the path
export HAXEPATH="$DIR/haxe-bin/mac"
export HAXE_STD_PATH="$DIR/haxe-std/std"
export HAXELIB_PATH="$DIR/haxe/lib"
export NEKO_INSTPATH="$DIR/neko-mac"
export NEKOPATH="$DIR/neko-mac"
export PATH="$HAXEPATH":"$NEKOPATH":${PATH}
Then you just need to do this
haxelib install actuate 1.8.6
(I specified 1.8.6 because that was the last version we used with Stencyl. You could also leave out the version number and just get the latest version).
Finally, in Stencyl, in Settings > Advanced > OpenFL Settings, add the following line:
<haxelib name="actuate" />