As of 13w16a the custom health option doesn't work anymore.
How to reproduce,
-create a custom spawner using NBTExplorer or the NBTEdit mod
-make the spawner spawn villagers with the TAG_Short 'health' set to 0
-You will see the villagers will stay alive
in 1.5.1 and 1.5.2 the villagers will actually die. So this bug will break all pre 1.5.2 maps.