I have placed a hwic-4esw in my 2801.
I've created a subinterface and assigned that switchport to that vlan. I have then connected it to my 3750. I can see the link in cdp. I can even see the mac of the hwic-4esw in my 3750 mac table, but nothing more than that. I've attached the configs.
no interface FastEthernet0/1.75
interface Vlan 75
ip address 10.10.75.22 255.255.255.0
no ip redirects
no ip proxy-arp
no cdp enable