Thanks Duncan for the clarification.
The link provided by Yezdi (http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002117) has an error in it where it says, with respect to das.usedefaultisolationaddress, that "You must set this option if you are setting multiple isolation response addresses."
Your document indicates that you could keep adding das.isolationaddressX values without the need to set das.usedefaultisolationaddress to false so long as the default gateway is pingable. Having read your book and knowing the knowledge that you have in this area I'll go with your analysis! :-)
Cheers.