I think that situation is simpler, and is just as you
surmise -- you
can't redistribute a plugin that claims to be under the GPL if it uses
the VST SDK headers.
There _are_ some VST plugins out there that use the SDK but claim to
be under the GPL, and I think that is really borne of frustration with
the current impossibility of "doing it properly" because of the
restrictive license for the SDK headers (most painfully, the SDK
license's reverse-engineering clause effectively forbids publishing
source for a plugin that _doesn't_ use the SDK, if you have already
accepted the SDK license).
The PC itself famously became an open platform after Compaq clean-room
reverse engineered the BIOS. This is considered legal - Someone who has NOT
agreed to the VST SDK license can re-create headers that mirror the function
of the VST SDK. They must do this by examining/debugging a running VST Host,
not by looking at copy of the original SDK.
You can't include the official VST SDK in a GLP plugin or host.
Jeff McClintock.