yes - the two subnets have to be able to communicate with each other for HA/DRS to work --
--> how about disconnecting the host from the VC - removing it from the existing cluster - chaange the ip address on the SC without a reboot - and then create a new cluster(make sure DRS rules and any other custom settings like resourcepools are transferred) and adding this host to the new cluster and then repeat the same process for all the hosts ?
once you make sure that the hosts are up in the new cluster -- you can test if this works post reboot by putting one host in maint mode ....
HTH
~Sai Garimella