Yes, Alexa can interact with SmartThings scenes. There is some overlap between the Alexa & SmartThings apps, which are outlined below. These comments are based on the v2.13.0 of the SmartThings app and v2.2.886.0 of the Alexa app.
SmartThings offers 3 main features: Things, Rooms, and Scenes. Alexa offer 3 main features (within the Smart Home menu option): Devices, Groups, and Scenes. These two sets of features are related but have some differences:
- ST Things and Alexa Devices both represent individual IoT devices in your network. When using a ST hub, you should first add the device to the ST app by choosing "Add a Thing" from the "Things" tab. Once added, rename if desired. Then go to the Alexa app and choose "Add Device" from the "Devices" tab. Alexa will scan for devices - including asking the ST Hub for a list of available devices. Adding to ST first ensures that Alexa talks to ST for all device interactions, and helps keep the device names in sync between ST & Alexa. However, If you change a device name in ST after adding the device to Alexa, the name change does not appear to automatically sync to Alexa.
- ST Rooms and Alexa Groups are both ways of grouping devices together, but there are differences. It's not clear to me if/how Alexa can interact with ST Rooms - I have not found a way to do so. Alexa Groups can include Echo devices, which causes that echo to prioritize the devices in the group. This lets you tell the Echo in your bedroom, "Alexa, lights on," without it asking you which lights you mean. You can even add multiple lights and Alexa will control them as a group. See this question for details. Also, a given Echo device can control a group even if the Echo isn't in the group.
- Alexa Scenes are directly imported from ST Scenes; once you've created a scene in ST, choose "Discover Scenes" from the Alexa "Scenes" tab to automatically import the new Scene into the Alexa app. Once imported, Alexa can interact with these scenes by name (e.g., "Alexa, turn on Bedtime").
It's also worth noting that Rooms/Groups and Scenes are similar, in that both group devices together. The difference seems to be that a scene includes not only a list of devices but also specific settings for each. So if you have an Alexa Group named "Bedroom" with "Overhead Lights" and "Closet Lights" in it, you can only turn "Bedroom" on or off, which affects both lights. But you can create a Scene called "Bedtime" which turns off the closet light and sets the overhead light to 10%. If you just want a way to turn on or off a bunch of things at once, an Alexa Group may be quickest solution. If you want more fine-grained control, create a ST Scene and import it into the Alexa App.
Finally, Alexa has recently added "Routines", which are a sequence of steps executed by name and which can contain Alexa skills in addition to home automation. For example, "Alexa, Start my Day" can fire the "Start My Day" routine that turns on the lights and reads the weather and daily briefing. This feature is a separate app screen/menu item, but can control devices, groups, or scenes configured in the Smart Home screen. Routines can also have custom invocation phrases. For example, you can create a routine named "Bedtime" that turns on the Scene named bedtime; you can then set the invocation phrase to, "Alexa, it's bedtime," or, "Alexa, Goodnight," instead of needing to say, "Alexa, turn on Bedtime," which is a fairly awkward phrase.