While a few people say they've kept guppies and bettas together successfully, bettas tend to be aggressive around other fish, in my opinion. It's especially true if the other fish have nice, big, flowing fins and are colorful: like guppies. It's just easier for the betta to confuse it for a rival.
In my experience, I had a betta that I tried to put in a community tank and he got aggressive toward anything that moved, no matter how different it looked and acted compared to himself. I am never going to try to put bettas in with other fish anymore myself.
So you can risk it if you want, but I'd bet 98% it won't work.