RCA's DSS codes operate on a 56 kHz carrier, a little higher than most (36-40 kHz) but Pronto will work just fine. If it doesn't catch it first time, just try it again. Other brands of DSS receiver are at 38 kHz, Sony is at 40 kHz.
By the way, some brands of cheap compact flourescent tubes (not those made by Philips!) emit a fair amount of IR energy around 50 kHz, which interferes with RCA DSS remotes, so check that the original remote is working OK before teaching the Pronto.
Philips site for Pronto is at www.pronto.philips.com
Garage door openers actually operate in an 'unlicensed' VHF band (around 318 MHz if I remember correctly). But the modern ones use a 'rotating polynomial' system that can't be cloned in that fashion anyhow...