Well, there is Sun's ongoing refusal to answer questions like "Are you willing to grant a license to any ZFS patents you hold to other FOSS implementations?", which creates at least a cloud of uncertainty about what they might do if they became evil, or just decided that Linux was catching up with Solaris and threatening them.
Unless they have changed their mind and answered this at some point. I hope so -- haven't followed closely.
But paulj is right re: copyrights; Sun wrote the CDDL in such a way that combining CDDL and GPLv2 violates the GPL but not the CDDL. This has the same effect in practice as not granting permission, but it means that for copyright issues we don't need to worry about Sun-turns-SCO -- we need to worry about SCO-turns-SCO.