ok, the word arpeggio has been and continues to be misused in terms of guitar. An arpeggio is merely the 1st, 3rd, 5th, and octave (1) of a triad played in succession. Sweeping does not necessarily equate an arpeggio...
There are two different schools of thought on sweeping, one is bending at the elbow and keeping your wrist and hand stationary, the other is bending at your wrist. I personally use the elbow motion one because the wrist needs to bend alot more to cover all the strings as opposed to the elbow. This creates more propensity for error with the wrist. Especially because muscular movement is most accurate and can be more finely executed in the middle range of the movement of the muscle. I.E. the wrist has to bend almost it's entire muscular range to cover all 6 strings, while the elbow needs merely a fraction of its range to cover all 6 strings, ie, you will have more control with your elbow.
I however, am a minority in this technique because alot of people get elbow injuries from doing this incorrectly, usually because of too much muscular tension. So do whichever way you want, but practice is essential.
As far as your left hand goes, DO NOT "roll" your hand, perhaps that's not the word you were looking for metal chef? Your left hand fingers should fret the string exactly as it should at any other time, with pressure perpendicular to the neck.
Sorry this was long, hope it helps.