I am running UI5, Vera firmware 1.5.622, Z-Wave 3.20, and Multiwave firmware version 3.4. I don't have everything working yet, but I was able to successfully add the PE653 to Vera and Vera can control the 5 circuits. She can also display the temperature. I have a Pentair VS pump, and Vera cannot control my pump yet. I have also been unable to make my PE953 a secondary controller, but I think I can fix that if I spend a little more time on it.
I wouldn't say it is easy, but it does kind of work, and Intermatic claims that firmware version 3.5 is coming out soon and will function much better with Vera. Their timelines are not very accurate, but I don't think they have abandoned Multiwave yet.