One of the nice features of the combination Vegas Pro 13 and Hitfilm Pro 3 is timeline integration.
When you right click a clip on the timeline you 'll see a menu with "Add Hitfilm Effect". After selecting it, Hitfilm Pro 3 'll start with your clip. After manipulating the clip in Hitfilm and hitting "save", you 'll return to Vegas Pro. The clip on the timeline 'll be updated with your manipulations in Hitfilm (2 directions integration).
The (current) installer of Hitfilm 3 Pro has only an option for integration with Sony Vegas Pro 13. The current release, Hitfilm 4 Pro, 'll install the timeline integration in Vegas 14. But at the moment I am satisfied with Hitfilm 3 Pro. It is not likely that FXHome 'll release a new installer for the older product.
Based on some investigations from others people (they tried to add timeline integration with MovieStudio) I managed to add Hitfilm 3 Pro timeline integration with Vegas Pro 14 on my system.
On my website you can find the instructions if you want to try it yourself.