The person who helped Rand was tall and could have been Logain apart from the fact that Rand could not feel him channel. Lets look at this a little bit more closely. Logain had been severed from the source and the reattached by Ninaeve. the question is which side of the source was he reattached to, maybe he's using saidar now. Note that as soon as he was healed Ninaeve could feel him start to channel which should not have been possible if he was using saidin. My theory is that the person who helped Rand was Logain and that his healing by Ninaeve has somehow altered his use of the source to make it undetectable by other male channelers. He is the most likely candidate to be lurking around Shadar Logoth.