Could an asteroid impact cause radioactive fallout?

I'm not aware of any relevant uranium ore deposit, which is related to meteoritic material.

Dangerous fallout is by far the most caused by short-lived radioactive isotopes. Those isotopes are rare in meteorites as well as in rock on Earth.

Natural nuclear reactors, which would produce short-lived radioactive isotopes, don't occur any more on Earth, since the natural U-235/U-238 isotope ratio is too low, now. This is due to the half-life of U-235 of about 713 million years in contrast to 4,468 million years for U-238.

If an asteroid would impact into a uranium ore deposit, most of the molten ejected material would fall back to Earth as tektites.

Evaporated ejecta and aerosols (dust) would probably increase health risk for some time, until it's washed out from the atmosphere. But other, less-radioactive aerosols would be a health risk, too.