Can I use a key switch rated as suitable for 12 or 24V DC with an Arduino?
These key switches are just a regular switches, and the specified numbers are just upper voltage/current limits. It should work fine with Arduino.

The main possible problem is that a dirt (or grease) on the contacts may present some resistance, so if your Arduino is too sensitive it might accidentally register switch as closed while it is actually open. This is likely will not be a problem until the switch spends some time outside, under dew, rain and snow, but if it does become a problem, add a smaller pull-up resistor. The Arduino's integrated pull-up is 20-50K, and you may want to add 0.5-1K if you have problems with moisture.