No - They’re not compatible with S2.

No, the gen 1 PLAY:5 is S1 compliant only. The gen 2 is S1 and S2 compliant. The gen 3 (The Sonos Five) is S2 only.

Both correct answers above mine, however, it depends on what you were asking. If you are trying to use the S2 app with the Port and the Play:5 gen1s both showing up as two rooms, than the answers are correct. The Play:5 gen1s can’t be added to the S2 app, but you could use the Port with the S1 app.

Now, if you wanted to use the Port’s line out with the Play:5 gen1s to send the audio to them using the S2. Basically treating the Play:5s as any other type of speaker connected with the Port, than yes.