Nate30.. Tis not a but-plug...Its a "BUG PLUG". Anyway the correct terminology is " Feed Thru Bushing" for those that are interested. And, it's not even for bugs.. It is used to keep the jacket on the RG intact when feeding thru an opening. You are correct however, it Should have a drip loop installed lower than the feed thru itself to keep water out.
This is CABL.com posting #211549. Tiny Link: cabl.co/m3cf