Sure, if that’s all you need, any two state device that can communicate with SmartThings can then be used for and “all on” and “all off.” It’s also much simpler since you don’t need load control. 
In this situation, many people would just use the Linear/GoControl auxiliary switch. It looks just like a regular switch but it is not designed to control the load. When it is pressed on, that signal is sent wirelessly to the SmartThings hub, and at that point you could have it do you anything you want that SmartThings can do, including turning on any combination of other SmartThings – controlled devices. And the same thing with the off.
https://www.amazon.com/Linear-Z-Wave-3-Way-Accessory-Switch/dp/B00EAY3K5Y
I wrote the following before I saw the two posts just above mine, so they don’t really apply to your situation. But I’m going to leave this text here because it might help someone else.
Alternatively, you could use a switch which allows for double tap, in which case tapping the top of the rocker once does one thing, tapping it twice does something else, and with some switches there is even the option of triple tap. So that’s another possibility, Although it’s less intuitive for guests.
You can also use any of many battery powered button devices. These work very well for scene control in SmartThings. For example, there is an eight button remote tech device which is about the same size as a regular light switch, although a lot of people mount it horizontally. Each button can be pressed, double pressed, or long hold which gives you a total of 24 scene options for the one device. It’s quite popular.
There’s also a five scene battery operated device which some people like:
Both of these and several dozen more are discussed in the buttons and remotes FAQ. That covers both battery operated and mains powered devices, and both wall mount and handheld:
I just mention all of that because I know you had asked a general question about scene controllers in another thread. To be honest, I didn’t respond in that thread because there are seven or eight different issues involving “scene controllers” and SmartThings, which is probably why you found some of the discussions confusing, but I also just didn’t want to start down that rabbit hole. There are issues involving load control and there are issues involving the fact that major manufacturers are just starting to come out with zwave plus versions of their devices, so some of the most popular ones in the past are no longer available while the new ones may not have come on the market yet. It just becomes a very long and complicated discussion right now.
However, for the situation you’re describing here, which is much simpler, just the gocontrol switch is probably all you need. I really just wanted to mention the FAQ and the battery powered options as well in case you did want to expand into more than just the two scenes of all on and all off.