No, beta testing for Android versions is for the upcoming version. You install the beta version of the newer Android version on your own device. It's not recommended for novice users, nor is it recommended for people to use on their daily driver phone, since there can be significant bugs.
I think beta testing for upcoming phones from any manufacturer is done in-house by employees. I'm not aware of any company that offers prototype phones to the public to test (although Google sure seems to "lose" a lot of their in-development phones, which then show up on eBay ...).