Is it possible to create a mission in Litchi export as a KML file and then import the KML into DJI GS Pro with all the waypoints?

Yes, you can do that.
You may notice that the expected results may vary, depending on your mission type.
For example, having a simple mission with 6 Litchi WPs, results, after importing into GSPro, in a waypoint mission consisting of 86 waypoints...

Please note that not all DJI aircraft are supported by GSPro.

Hi, thanks for the inquiry. We will forward your query to our team if this could possibly be done, however, as Keule mentioned, there will a list of compatible drone with our DJI GS Pro as well.  GS Pro is supported on all iPad Air, Air 2, Mini 2, Mini 3, Mini 4, and Pro tablets (Android is currently not supported). GS Pro supports the following DJI aerial platforms and flight controllers: Phantom 3 Standard、Phantom 3 Advanced、Phantom 3 Pro、Phantom 3 4K、Phantom4、Phantom 4 Advanced、Phantom 4 Pro、Phantom 4 Pro V2、Inspire 1、 Inspire 2、Matrice 100、 M200 Series、Matrice 600 Series、Mavic Pro、A3、A3 Pro and N3. Please let us know if you have other concern. Thank you for the support.