this is not official and I do not speak for HSX but I believe this is how it goes:
DMac's link to the terms of service (that islander linked to) implied that traders are not to have more than one account for the purpose of manipulating the stock prices.
DMac has stated in the past that HSX "overlooks" players having multiple accounts if they are clearly not used for stock price manipulation (by trading different stocks, having different strategies, YTD ports, etc...)
It is my opinion that DMac/HSX say as little as possible about issues because there are several players who then hold DMac/HSX to the letter of what they said and if something is said wrong or something is said but then later changed, the troublemaking players attack DMac/HSX with it and try to hold them to what was said... so DMac/HSX say as little as possible.
The reply that islander linked to was DMac's response to a player who admitted to having 4 different ports and the wording of that players post made it sound like he could using the other ports to group trade to benefit his main port:
"if you've been on here making trades, trying to gain H$ with a few ports, at least that should be an option so that the port(s) you don't use as often don't get penalized with the non-usage fee they're bringing in"
Each player should only have one account and be focused on growing it. Funds have specific trading guidelines to go with their themes that makes it hard for managers to use funds for manipulation. YTD ports are usually clearly marked giving HSX a heads up what the port is being used for. Other than that, there are very few exceptions why players would/should operate more than one regular account.