I have several ISR one's i.e. C2801 and C1841 in my network.
They are deployed with HWIC ethernet switch modules:
HWIC-D-9ESW - C2801
HWIC-4ESW - C1841
I seem to be unable to discover end hosts connected directly into these ports.
If I have a switch connected to the HWIC ports instead and the end hosts resides in the ports in the switch there are no problem.
Routers are managed all right in all other matters.
I think this is a design issue the UT is not done on router ports, and that the HWIC are treated at router ports instead on switch ports.
How can I do UT on HWICs ?
You are correct. UT does not support switch ports on routers. Support for the BRIDGE-MIB has only recently been added to those platforms (in 15.x code), but UT has not been updated to treat those routers as potential L2-capable devices. There is no workaround for this at this time.