OK, thanks for your input, that helped a lot. My main concern was if a setup like this is supported by VMware.

I think we will only use the Enterprise version, so we would have to go with Standard vSwitches. Using the described setup with a different active preferred uplink for the portgroups seems to be a good idea. Just to sum it up, you would recommend the following:

Portgroup: iSCSI -> preferred active uplink NIC1, standby NIC2

Portgroup: vMotion-> preferred active uplink NIC2, standby NIC1

Portgroup: customer-LAN-> preferred active uplink NIC2, standby NIC1

Kind regards