Hi BBoy…
SmartTiles (and ActionTiles, coming soon_ is limited to the functionality of a SmartApp, not a Device Type Handler. They are two distinct concepts in SmartThings.
SmartThings does not expose the full customized functionality of a Device Type Handler to SmartApps … no… only the official Capabilities, and the list of any ad hoc Commands and Attributes. SmartApps don’t get access to the metadata that defines the special tiles that you see inside the SmartThings mobile app Thing detail view, for example.
(Maybe SmartThings will eventually change this… enhance the Device API…).
In order to get ActionTiles released, we only support Capabilities official definitions; but as we identify certain popular officially published and approved “Works With SmartThings” Device Types, we will consider adding them on a one-by-one basis.
In your example; Ecobee works with SmartTiles because it conforms to “Capability Thermostat” (and a couple other standard Capabilities). Rain Machine, I think, “irrigation controller” (right?) and SmartThings does not have any such standard “Capability Irrigation Controller” yet … if ever.
###The current workaround?
Virtual Switches, Buttons, (etc.) can be used and kept in sync with a SmartApp. Then these Virtual Things can be added as Tiles to SmartTiles/ActionTiles.