There are no specific hardware requirements for UUCP under Linux. Basically any Hayes-compatible modem works painlessly with UUCP.
In most cases, you'll want the fastest modem you can afford. In general, you want to have a 16550 UART on your serial board or built into your modem to handle speeds of above 9600 baud.
If you don't know what that last sentence means, please consult the comp.dcom.modems group or the various fine modem and serial communications FAQs and periodic postings on USENET.