Oh yea, they definitely do. I question the quality of a lot of the products that work with Alexa, but that's really up to the individual to decide. I found Siri to be the same as Alexa in a lot of ways, they just need to open it up on the HomePod also. The Siri Shortcuts app in iOS 12 will help with anything more advanced that I need Siri to do.
In many cases they are the same products you would use with HomeKit. Question all you like, but if you want to automate things you are going to have to rely on 3rd parties anyway.