No, the Grebulons are just an innocent group of people who got sucked into the whole "blow up the earth" thing by Scary Bird Thing.
So what do the Vogons have to do with it? Hold on, I'll find the relevant passage. . . Okay, I found it.
In the darkness of the bridge at the heart of the Vogon ship,
Prostetnic Vogon Jeltz sat alone. Lights flared briefly across the
external vision screens that lined one wall. In the air above him
the discontinuities in the blue and green watery sausage shape
resolved themselves. Options collapsed, possibilities folded into
each other, and the whole at last resolved itself out of existence.
A very deep darkness descended. The Vogon captain sat
immersed in it for a few seconds.
`Light' he said.
There was no response. The bird, too, had crumpled out
of all possibility.
The Vogon turned on the light himself. He picked up the
piece of paper again and placed a little tick in the little box.
Well, that was done. His ship slunk off into the inky void.
In spite of having taken what he regarded as an extremely
positive piece of action, the Grebulon Leader ended up having
a very bad month after all. It was pretty much the same as all
the previous months except that there was now nothing on the
television any more. He put on a little light music instead.
I don't understand how these two passages fit together. It makes no sense. . .
I googled this passage because I was too lazy to type it up, and found the complete text of the HHG trilogy online. Weird stuff.