ALL Tangs are ich prone. Some more so than others (the Powder Blue is probably the most infamous for it), the reason they suggest not with inverts is in the event you want to treat the tank to kill the ich, but you wouldn't treat your main tank anyway so....So IMHO no there is no substance to the belief. Just ensure you have tank that is OVER 6 months established and they shouldn't get ich period. Anyway hope this helps and good luck!