This is more out of interest for others than for personal use, as my Soulstone alt is on the same account as my main (I just log onto my alt and trade Soulstones with someone else rather than SSing myself).
But, as you can see below, these are two directly contradicting messages regarding dualboxing a SS alt:
viewtopic.php?f=76&t=28165#p197262
"Violation of the rules" vs "It should be okay."
PS Screenshots aren't mine.