Unfortunately, because VirtualHostX requires your administrator password to make changes, there's no automatic way to sync your virtual hosts. However, for the very technically inclined, it is sort of possible using Dropbox. Here's what you'll need to do:
Setup a symlink to sync the following folder and file through Dropbox
Make sure to only run one copy of VirtualHostX at a time - otherwise you risk corrupting your data or losing changes.
Please note, while I'm happy to offer advice on this topic, I can't officially support anything that goes wrong :)