I randomly ran across these examples of Roman-migration period spathae with rivet-holes in the tangs. http://museummilitary.com/en/section_20/weapon_52 http://museummilitary.com/en/section_20/weapon_51 http://museummilitary.com/en/section_20/weapon_8 I have not seen this characteristic before. Has anyone seen any other examples? There are no rivets in the holes, wooden rivets maybe?

See this thread:
http://www.myArmoury.com/talk/viewtopic.php?t=26777

Mart that is a good possibility. All of the complete ring-hilts shown have welded or brazed pommels, and I assumed that those that had riveted-on pommels would have squared off tangs, but you know what they say about assuming. Also, the examples I linked to only have one rivet hole while the ring-hilts require two. Or do they?

I guess it is a possibility, but later Hunnic swords have a similar tang hole but are never associated with the "Sarmatian / Roman" ring pommel.

The sword with the hexagonal blade doesn't look like the typical Hunnic sword to me, but the one with the octagonal blade comes close. Without at least the find place and some context it's difficult to say for sure. And swords from the greater Hunnic confederacy can be pretty varied.

As for the Hunnic swords, I don't think there is consensus on the exact form of the hilts of these swords. Personally I believe it's likely that the hole was there to accommodate a cord (or hand loop) to which the sword bead could be attached.