Well the FF are basic stock characters, so its not unusual to see some or all of them in other places. Though if you read the first issue the characterizations we know so well hadn't quite firmed up. Ben especially isn't quite the idol of millions we've come to know. There's no trace of his classic speech pattern and his favorite word seems to be "bah!" Sue doesn't come off as shy and Johnny seems more impulsive that hot headed. Ben's more of a hot head anyway. (Anger control ain't his forte.)
I don't see why Ben wouldn't use the word "dude". He's not exactly the type to avoid slang. As for Reed being a nerd, yeah he is one. Though, back in the early 60 Ben might have called him an "egghead". Same thing, really.