I have same trouble.
But i think there is a way to solve it.
As we have access to filesystem, we can make chroot, then we can try to install vmware tools and all depencies.

I think open-e dont include vmtools in the distributive because of vmware change vmtools version with products releases and open-e dont want to rebuild distributive every time when vmware products updates - so its right decision.

BUT

I think if Open-E include some way to install vmtools - than dss will be more useful.
So at this time i'm continiue to evaluate and searching for another products.

For example FreeNAS 8 have vmtools installed. But it missing some functionality that i need.