This Vundle compatible Vim plugin provides syntax highlighting and dictionary completion of built-in function names for Side FX's VEX programming language.
For information on using dictionary completion in Vim, run :help dictionary.
The syntax file itself is the same file that ships with Houdini and is located in
$HFS/public/syntax/vfl.vim. Side FX put this file in the public domain which I confirmed
via their customer support (Side Effects Support Ticket 77542).
The dictionary is created with:
vcc -X surface
which you can run inside shell from Houdini main menu > Windows > Shell. More information on this process is in the SideFX forum.