That seems like a reasonable goal.
Just realize that because there is no direct integration between Leeo and ST, it’ll take a little work to set things up in such a way that you can see a device that looks like a smoke detector within ST. But with IFTTT and the universal device type handler described in the posts that JD linked to above, it’s definitely possible.
I think it’s also important to point out that the more cloud-based services you link together in order to receive an alert, the more potential points of failure you can run into. You’d be relying first on your Leeo device to work correctly and send an alert to the Leeo server, which then has to communicate with IFTTT’s server, and then in turn with ST’s server. For something as critical as a smoke or CO alarm, that’s not something to take lightly.
I still have Leeo setup to alert me directly from their app if the sound of a smoke or CO alarm is detected, even though I’ve also integrated it into smart home monitor. I even got a kidde remotelync too, which does basically the same thing as Leeo.
I have kids and pets at home, if a smoke or CO detector is really going off while I’m not home, I want as many different alerts as possible with redundancies so a single service failure (hopefully) doesn’t screw up the whole thing.