I mean I hope. I am sure they have been in some loud stadiums before, but this will be playoffs time. I am sure Highmark is sold out and fans outside will be crazy. For reference, here are the away games they've played this year:
Jacksonville (Jags fans? please)
NY Jets (after Rodgers was knocked out)
Vikings (a little crazy fan, but mediocre team)
Broncos (during the skid)
Vegas (imported fan base)
Packers (lost)
Patriots (eliminated)
Chargers (eliminated)
So they have played one playoff team on the road, and that was a loss.
There is a case to be made that they are not road tested.