Thanks for the file.
Skatter is not actually freezing Sketchup. You have a lot of Skatter setups, some of them are taking a long time to compute. At Sketchup startup, Skatter re-computes every setup (otherwise if everything was stored in the file, the file would be huge), that's why it takes a long time to open your file (5 minutes on my computer).
The more geometry (faces, edges) in your surfaces/curves, the more time it takes to compute.
And obviously, the more objects scattered, the more time it takes to compute.
There is no way around it for now.
I will try to optimize this by not computing at startup the "disabled" setups.