D-He3 is a much more energetic reaction. So in order to produce 50 MWe, they need to have a certain amount of He3 in the fuel mix.
But their fusion generators can still produce a small amount of net electricity from just fusing D-D. Demonstrating that is the goal for Polaris from what I understand.
Half of the D-D reactions produce He3 and half of them produce Tritium. The Tritium will eventually decay into more He3, but if I was them, I would just sell the Tritium and buy more He3 with that money, rather than storing it for years (half life of Tritium is 12.5 years) to get more He3 that way. Both cost about the same (about 30,000 USD per gram). He3 is currently slightly cheaper, but it is a roughly equal trade.
Helion can balance the density and temperature pretty freely. To the best of my understanding, they are going for a lower temperature and higher density, which favors D-D reactions. The downside is more neutrons, but they think they can handle that.
So the short answer is: Yes, they can just produce He3 and Tritium with an otherwise self sustaining machine and make money from selling the isotopes.
Aside from demonstrating net electricity and increasing their performance and rep rate, Polaris will actually do just that (and likely set aside some He3 for test runs with that as well).