Drano can safely be used in the toilet but unless the clog is right in the toilet then the Drano will not work on the clog in the toilet.
The Drano uses heat and caustic or oxidizing chemicals to clear the clog and dissolve what is clogging the toilet or drain.
So yes it's safe to use the Drano in a toilet but it's not likely to clear the clog unless the clog is inside the toilet itself.
I would first try a plunger or a toilet auger first before trying to use Drano in the Toilet.