Aim and shroud the LEDs properly and it should work well. Aim and shroud them improperly and it will attract a lot of negative attention. LEDs are perfect for this type of application, but only if done properly. There is a reason they're used to backlight LCD displays..

For the record though, the dispersion pattern on those LEDs looks like shit, but that's because the license plate lighting wasn't designed for LEDs, and those LED bulb replacements aren't designed properly either. You should be able to find better products that do the same thing; there are LED cluster replacements for most of the common accessory bulb sizes and many of them have very good dispersion patterns. Keep looking.