AFAIK, if you disable ALUA on the igroup and leave the PSP as VMW_PSP_RR then ALL paths to the storage will be used, i.e. the round robin policy will load balance across all paths to the LUNs including the partner paths and reduce performance. However, when you reboot your ESX(i) hosts they will detect that the storage is no longer supporting ALUA and change the PSP to the default for NetApp arrays without ALUA, probably Fixed. You can check the default PSP for each STAP using the CLI command
esxcli nmp satp list
If you are doing this from a remote CLI then add the servername in, e.g. esxcli --server esxi01.mydomain.local nmp satp list
You will need to manually set the default path for each LUN so that it is using a primary partner path and load balance them across connections. If you are using ESX (i.e. not ESXi) then you can load the NetApp ESX Host Utilities on the Service Console and then run a command to set the default paths to primary paths automatically for you.
I'm not sure of you really need to disable ALUA on the igroup. Are you attempting to add iSCSI initiators to the same igroup as the FC HBAs? You will need to create a new igroup of type -i and add the iSCSI initiators to that. You can then map all of the LUNs mapped to the existing igroup also to this new igroup, so you have the LUNs mapped to both igroups. I would make sure that you use the same LUN id on both igroups, even still you might encountered some problems for disk identifiers if you are using RDMs. If you have a lot of LUNs to map then you could do this fairly easily with PowerShell, let me know if you want a hand with the PowerShell script (we might even be able to do it with a one-liner - although a long one).