Dave, you are right, background delivery does not work with nsopenssl, there is no easy way to address the problem. The best approach is to deactivate it automatically, when a request comes via SSL.
I was not aware about the flag UseBackGroundDeliveryP, and did some history mining. The flag was introduced by Mannheim in 5.2 (as parameter with code in revision_procs), but then the changes were reverted soon after that, but whoever did the revert missed the flag in the kernel parameters.
http://cvs.openacs.org/cvs/openacs-4/packages/acs-content-repository/tcl/revision-procs.tcl?only_with_tag=oacs-5-2
It is better to deactivate background delivery automatically in cases where it is known not to work, than to depend on an admin deactivating it manually.
i have made this fix in cvs head, oacs-5-4 and oacs-5-3.