It sounds like we are mixing apples and oranges here, but maybe I am just confused. 
I am not aware of any “friends of Hue smart button.“ There is a Phillips hue smart button, but it is not a green power device, it has a battery. So it would be off-topic for this particular thread. If that’s the one that you were talking about, please start a new thread for it and we can discuss what might be possible.
This is the one that I am referring to:
https://www.amazon.com/Philips-Hue-Button-Control-required/dp/B07XV1HRVZ/
If there is instead a green power smart button from another brand, please let us know the brand and model. In that case, it should run into the same issues as the “friends of Hue“ batteryfree Switches.
Green Power Devices and SmartThings”
If there is a way to get around the missing platform features, it would be with a DTH (device type handler), not a smartapp. You would have to be capturing the raw message stream from the device and then convert it to somethings smartthings could understand.
However, before you can do that, you have to have connected the device to your smartthings zigbee network even if it’s just as a “thing.“ And my understanding is that that is not possible with green power devices right now. If you can’t even connect it as a thing, then there’s nothing you can do just with code.
There is an additional issue which is that green power devices, unlike most others Zigbee profiles, do not check in on a regular basis because they don’t have any power until someone presses them. So even if you do get them to add as a thing, one of my concerns would be that it would be marked as “off-line“ until there is official support for this stack. That might make them unusable with SmartThings.
My guess would be that you can connect the smart button, which again, is not a green power device, as a thing, but you cannot connect the batteryfree devices at all.
Green Power Devices on a Hue Bridge without HomeKit
There is another possibility, which some people have done with the hue tap (another green power device). That is to connect it to a hue bridge and then poll the bridge “heartbeat“ for activity. But for some technical reasons you probably also have to have a Hue motion sensor connected to that bridge and this method has not been very reliable in the past. And unfortunately that method seem to have broken about a year ago. But here is the link to the thread if anybody wants to take a look:
Green Power Devices on a Hue Bridge with HomeKit
The most reliable method right now would be to use homebridge to expose your smartthings devices to apple’s Homekit and then use HomeKit to create rules for the green power devices. But that’s a lot of work and requires an additional server. It’s not something I would recommend just to get those devices, it’s only something to consider if you are already using homebridge.