Hmmmm....

I think the dagger could indeed make Mat invisible to the gholam, in the sense that he would have no way to even know what's attacking it, or to defend himself.

I think it's very possible if the gholam is killed this way, then the medallion will be destroyed in the process. I think we might be looking at something in the vein of the SL evil vs. the DO's evil there.

As for the blunt dagger.... if it's used with the gholam, it won't be used at SG too. Now that I've read and pondered your idea, I'm more convinced than ever that the whole "and maybe Shai'tan's attention too" bit was a red herring. That's classic Jordan. He attracted our attention on the "big thing" to hide the small thing in plain sight: this dagger will protect someone from Shadowspawn hunting them. He did the very same thing about the CK by the way. From the start he let us believe this was a weapon with which to challenge Shai'tan, men and women together. This distracted us from the fact the most powerful circle possible was used to cleanse the taint from a small quantity of saidin, and if Rand was to cleanse the whole, he'd need something like the CK, and a woman.

In a similar vein, I think it's quite possible it's not Callandor and two women Rand will use at SG. Again, it's too obvious (when the characters start making theories on screen the reader already figured out... something is fishy) I think it far more likely refers to Justice and Perrin and Mat (and the colours). There's something special about that sword that "LTT" knew about and didn't tell Rand. Beside, we have been told now that channelling against Shai'tan = not an option.

Most of all, I just don't think Rand will sneak up on Shai'tan. I don't think taking Shai'tan by suprise would do any good.