sense that a virtual machine's nic (virtual port) gets connected to a virtual bridge, so multiple virtual ports should be able to connect to a virtual bridge
That's one way of looking at it. But technically, a VM's vNIC attaches to a virtual port on the vSwitch. It doesn't attach to the vSwitch itself.
In RackTables you can add multiple ports of the 'virtual port' type. Add many of these to your vSwitch and one or more to each VM, then link them as you do physical ports.
-- Aaron Dummer