Consider the fact that such knowledge plot wise would have made it easy to capture Rand. If Rand can use Moridin's power than Moridin can certainly use Rand's. Consider how LTT took control on that one occasion. If Moridin took control of his power on purpose he could easily kidnap Rand.

Of course it might be the desperation that made it possible and there is no reason that Moridin should have ever been that desperate to find out.

Of course this link might be the real reason for Rand's channeling sickness. Reaching for the source from two different locations.... i think I may have just given evidence for how Moridin could have known but Rand couldn't.... he never channels the OP only the TP so Rand would never have reason to know someone was trying to use his connection.... I still don't think Moridin purposefully created a circumstance where Rand would use the TP. It would serve no purpose unless there was some long term benefit to that one time use. So far no such benefit is in evidence and none have been proposed. Semirhage's torture of him is significant cause for his mental break and would have been sufficient without exposure to the TP.

by the by i doubt you have to ask permission for each use of the TP. Moridin was allowed access and unless and until he proved disloyal the opportunity would not be denied.