After reading this thread a while back I decided to see if it was possible.
The candidates: a dwarf gourami and a very docile crowntail betta.
I tried putting my crowntail betta in with my 10 gallon, which has a female dwarf gourami in it. The betta was immediately chased around and hid alot, so about 30 mins of watching I took him out.
So I decided to try it the other way; I took out the dwarf gourami for 3 days and put the betta in, to let him get accustomed to the tank. I then put the gourami back in, watched them for about 30 mins, and had to go to work.
I left for work at 10AM and it's now 9PM and neither of them are showing any sign of a fight. They were on opposite sides of the tank, and when I tapped the glass to make sure the betta was alright, he came out to the middle, saw the gourami, and flared at it, following her, but never did he attack or chase her. He has just been kind of watching where she's headed and going back to his own business.
So I agree with echoofformless, that keeping the two together is possible, but you just need to be careful!
In the end, I'm still worried about the betta pestering her, so I took the gourami out just incase.