Do you mean routed or switched? Hardware offloaded routing is experimentally supported in RouterOS 7.1-beta for some CRS3xx devices. In RouterOS 6 hardware offloaded switching is shown under Bridge > Ports by the H flag when active, routing traffic between different VLANs is always handled in software.
In winBox, all of my VLANs are listed in the “VLANs” table under the “Bridge” window. It will function this way, but in order to assign an address for the switch under a particular subnet, I appear to need to also set up the VLANS in the “VLAN” tab of the “interface” window, and then assign those VLAN interfaces to the bridge as well. Is this correct?
A bridge has multiple roles, see http://forum.mikrotik.com/t/routeros-bridge-mysteries-explained/147832/1 for a good explanation. Interface VLANs just add a VLAN tag in one direction and remove it in the other - they should use the bridge (interface-like role) as the parent interface, do not add them as bridge ports.
If I switch to using swOS and set up the VLANs there, will the VLANS set up under swOS take advantage of the hardware offloading? Is there any performance disadvantage to using swOS?
I believe swOS always uses hardware switching. It only performs switching so you can’t use any other RouterOS features, e.g. DHCP server, Management communications and configuration backup files are not encrypted.