Chris Coste is a 33-year old rookie just now getting his first taste of the Major Leagues. While he is definitely a feel-good story, I don't forsee him as a reliable fantasy option at catcher. However, he did have a career year at AAA last season, batting .292 with 20 HR and 89 RBI, so I suppose there is a SMALL chance that moderate success could continue, given sufficient at-bats. I definitely wouldn't bet on it, though.
FWIW, Coste was batting .177 with 2 HR and 14 RBI in 147 AB at the time of his call-up.