You can add 2 Play 3s to the beam as surrounds and that will get rid of the delay that Chris mentions you would have if you GROUPED a Play 3 (or a stereo pair of Play 3s for that matter) to the Beam. This is because the surrounds are designed to play the video audio channel so don't delay the audio.
I would have thought that if you have a Beam and Play 3 in the same room and the Play 3 is playing the same audio as the Beam but 70ms behind it that would be horrible. But if, say, your Play 3 was in the kitchen and you wanted to continue listening to the TV whilst there but you can't hear the Beam or see the TV it would probably be ok,
Arc + Sub (Gen 1) + 2 x Play 1/ Stereo Play 3s/ Era 100 Stereo in Kitchen, One Stereo in Bedroom, Play 1 stereo pair in Study, Play 1in Bathroom, Sonos Move 2