my thought on 2-halo-succinic was in regards to malic so isn't entirly relevant here.
but for the case of 2-halo-succinic acid is the Hell-Volhard-Zelinsky going to give you any 2,3-dihalo-succinic, or is the 2-halo suffeciently deactivating to keep the 3 halogenation from occuring?