@Ronnie @blew888 @David_Waters
Yes the app listed here -
does currently only support controlling the Velux blinds.
I believe the Tahoma system would be able to fully control the Velux windows but the above as mentioned is limited to the blinds. Indeed I found a post in the Somfy forum asking this and there seems to be a reply from Somfy saying yes. The link below is a GoogleCache one as just now at least the Somfy forum as not responding.
http://webcache.googleusercontent.com/search?q=cache:AuaVp4oY6vkJ:https://forum.somfy.co.uk/questions/1669201-can-control-velux-windows-velux-blinds-window-blinds-somfy-tahoma-app&hl=en&gl=uk&strip=1&vwsrc=0
So even though the above Smartthings app only supports blinds it sounds like it could be potentially expanded to support more functions via a Somfy Tahoma gateway.
The Velux windows can be controlled via the Netatmo Active interface which so far does not appear to have a Smartthings app but can also be controlled via the KLF200 interface. The KLF200 interface uses the io-HomeControl system supported by Tahoma. The KLF200 has an api documented here -
I believe the Velux windows can be controlled via Home Assistant using the KLF200 however it might also be possible by adding them as HomeKit devices via the HomeKit client (not HomeBridge). It then either way might be possible to share them to Smartthings via MQTT.
@NomadTech previously mentioned using a Logitech Harmony to use IR signals to remotely control Velux windows and I have seen on YouTube a video showing using a Broadlink IR remote system to do the same. There is built-in support in Smartthings for Logitech Harmony but there is also at least one community driver for Broadlink although this might also require a Raspberry Pi or similar.
The following is I believe for OpenHab but contains useful information if anyone is willing to create an integration between Smartthings and Netatmo/Velux Active.