Lesnod11, I don't know where you are getting your information but I can quote the proposed regulations. Bitcoin is my weekend/evening job; it's my business to know these things at a professional level. I don't intend to sound rude or condescending, but this literally is my 2nd job.
An entity can still do arbitrage on their own behalf - using their own money - but they follow a different set of rules when using someone else's money. Part 200.2(n) says that a "Virtual Currency Business Activity means the conduct of any one of the following types of activities involving New York or a New York Resident: ... [part 2] securing, storing, holding, or maintaining custody or control of Virtual Currency on behalf of others."
Then, 200.3 (a) states "No Person shall, without a license obtained from the superintendent as provided in this Part, engage in any Virtual Currency Business Activity."
So, any entity/person holding or controlling Bitcoin for a New York resident MUST have a license. Out of the hundreds of customers Btc-Arbs had, they almost certainly have at least a few New York residents. Btc-Arbs would also fall under the definition of the regulation in other sections as well. The full text is at http://www.dfs.ny.gov/about/press2014/pr1407171-vc.pdf
In order to avoid just that quoted section, btc-arbs would need to fully refund all New York residents before the regulation goes into effect. And even then, any of those residents could say that the claimed profits are still owed to them.