No. Separation discs and heterocysts are both different ways in which hormogonia are delimited - or separated from the originating organism.
A heterocyst finally breaks off from the filament causing fragmentation. These fragments are called hormogonia and undergo asexual reproduction.
A separation disk is a biconcave gelatinous layer found between two adjoining vegetative cells in some blue-green algae and associated with hormogonium formation.
This method of vegetative reproduction is found in blue-green algae. The trichomes of blue-green algae break up within the sheath into many-celled segments called hormogonia or hormogones. They remain delimited by the formation of heterocysts, separation discs or necridia or by the death and decay of intercalary cells of the trichome.