Na minha experiência, a resposta para a maioria das ervas aromáticas é sim, a fragância e o sabor são preservados. Nunca tentei hissopo, no entanto site de jardinagem sabe como diz que congela bem:
it can be dried or frozen and stored for later use. When harvesting a hyssop plant, cut it in the morning hours once any dew has dried. Hang the plants upside down in small bunches to dry in a dark, well-ventilated area. Alternatively, you can place the leaves in a plastic bag after removing them from the stems and place in the freezer until ready to use.