My gut feeling is the same as suggested by Dan. I feel that a hole would created a stress zone, that could lead to a broken oar, in a heavy rapid--oar flex situation. There is a hole for the blade, but the base insert tube of the blade supports this area, so the flex is above the hole.
The oar rights I have are for the right size oar. Maybe I will just cinch down the bolts tighter, or substitute the flat head bolt, for allen bolts. Perhaps adhesive under the rights??