The first one definitely isn't tautology, as "pretty" here is being used as an adverb, as in "pretty big", "pretty old". It just happens to be capable of being used as an adjective meaning "attractive", especially of women.
The second one is dubious at best. Just because something is horrific doesn't necessarily make it scary.
I'm guessing you've not read the whole thread, stewey. "Pretty" here is not an approximate synonym for "lovely"; it could be replaced with a similar word like "rather".