In my opinion, it's a poor idea.
The Thunderhawk is really more than capable of looking after itself, considering how heavily armed and armoured it is. Four twin-linked heavy bolters, a twin-linked lascannon and missiles also seems a little much for a fighter. The mainstay Imperial fighter, the Thunderbolt, only mounts a pair of twin-linked autocannons and a twin-linked lascannon.
If the Space Marines need fighter support, I'm sure the Imperial Navy will happily provide. Fighter crews aren't the place for Space Marines.