Isn't that like Pay to win?
Does it matter if it is?
Whether you are skilled or not at controlling two characters and if it's not cheating. There lies the possibility to beat content without others help regardless of your skill with one character, you could possibly not beat that content with one character.
Imagine a professional baseball player hiring help in the outfield to catch balls.
Is he rich compared to other players? Possibly.
In a fair competitive playing field, money should not come into play. Whether it's considered cheating or not is of no relevance. If everyone is not allowed that option regardless of income, then it's an un-fair advantage.
I realize that there is no way to stop this unless SE denied multiple accounts with the same IP. They won't go there due to wanting money and not wanting to restrict players form paying for what they want.
TLDR: It won't bother me in the slightest as long as my gameplay experience is not affected in anyway by those actions of others who do this.