I'd love an answer to this as well!

while i have not used butyl tape, if you have it and its convenient, it should work just fine.

in the drill/fill/drill method, the key purpose of the approach is to seal and protect from water intrusion, the exposed wood core of a glass/wood/glass sandwich that gets opened when you drill a hole into it.    

in a piece of wood that is glassed and waterproofed on each side, when you drill a hole, you reopen the core (wood) of this sandwich and now you have lost your waterproofing.   by drilling a larger hole than is needed, filling it with epoxy, and then drilling down the center of it with out touching the wood, you have now sealed the core from potential water damage.

so what purpose then is the 'dab of silicone'?   (which you are proposing be replaced with butyl).   well, in a through bolted situation, while your drill/fill/drill has protected the core, you still have a hole in the skin of the boat  (from the outside of the boat to the inside of the boat.. a good example being footbrace screws that go through the side of hull) that even when through bolted, can result in a leak into the boat because there is a little bit of space between the through bolt and the sides of the hole.  the dab of silicone's primary purpose in drill/fill/drill is to ensure you don't have a leak in your boat (vs protecting the core).

silicone can also backstop your drill-fill drill process if it was not perfect helping to avoid core damage....but this is a secondary and not primary purpose.

anyway, at the end, butyl tape can do this too.  i don't know that i would call it easier to work with for this particular operation because since you are using it to fill the space between the sides of the hole and the screw, i just dab the screw with silicone before installing it....which strikes me as pretty easy.   butyl tape is pretty convenient when dealing with seams ...and caulking kind of situations....but that's not what is going on here.  anyway, that said, it will work too.

h

   Thanks! In my case I also have some seams to seal for the inspection ports on my Passagemaker. So it seems like butyl would be easy to use there. Maybe less so on the other holes like rudder hardware and oarlocks.

the only other thing i would add on butyl tape is to be sure to read the manufacturer's specification. 

for boat work, i generally try to stick with marine grade materials, adhesives, etc, where they have been validated in marine/salt-water environments.

i suspect that there may be different quality/grades of tape....so if you are relying on it for something that is important on a boat, you just want to ensure it will perform as expected.

h