Yes, you can mix the platforms with HSRP, but you won't be able to support multiple HSRP (MHSRP) due to the hardware limitations of the lower-end platform (eg 7200 series can support it but Lance and QUICC ethernet controllers can't).
I couldn't find anything else you would need. Your mod would look something like this:
sup> (enable) show module
Mod Slot Ports Module-Type Model Status
--- ---- ----- ------------------------- -------------------
1 1 0 Supervisor III WS-X5531 ok
2 2 Route Switch Ext Port
3 3 1 Route Switch WS-X5302 ok
4 4 24 10/100BaseTX Ethernet WS-X5225R ok
5 5 12 10/100BaseTX Ethernet WS-X5203 ok
Steve
