There's a tradeoff involved here. On the one hand, blitz ratings tend to reflect a player's strength in blitz (by definition). But on the other hand, most players play many more standard rated games, meaning that rating could be considered more accurate.
In general though, standard ratings are a reasonable enough indicator of blitz results. Most players who are good tend to also be good in blitz, although there are of course exceptions (older players, for example).
Of course, if you're referring to online blitz ratings vs USCF standard ratings, the online blitz ratings are clearly a better indicator. People play far more online blitz games than OTB games.