If they show up as controllable in the Amazon Alexa app routines ( not a smartthings routine) , You can use That app as a “man in the middle” And get limited one way smartthings integration that way. (SmartThings Will be able to turn the switch on and off, but turning the switch on manually will not trigger anything in SmartThings)
The setup is a little weird because at present Amazon routines can only be triggered by either a sensor Or an echo button. Not a switch.
However, the good news is that that could be a virtual sensor from SmartThings. So you can create a virtual sensor, create an Amazon routine that starts when that virtual sensor is marked as open, and then use smartthings to change the state of the virtual sensor.
Like I said, it’s a little goofy, but it does work. And for something like holiday lights any brief lag shouldn’t matter.
See the following FAQ (this is a clickable link)
So that’s another option for some Wi-Fi plugs as long as they work with echo.