For a port mirror you will need to specify an additional port on the ESX server to receive the mirrored traffic. I don't believe you can mirror traffic to a vlan destination, because mirrored traffic is dead traffic. VLANs provide switching and lookups before forwarding, while dead traffic should just go out everywhere. Thus you are talking about 2 different functions of the packet processor.
Also I wouldn't suggest mirroring traffic onto a vlan and then sending it into esx via a trunk because it can oversubscribe the port and then you lose control traffic.
Again I'd mirror the traffic to a port, then connect that port to a different port on the ESX server with a separate virtual switch, and then tie the virtual IDS interface to that other virtual network.