Does thread compound (dope) over tape prevent this kind of leak?
You're supposed to use one or the other. If you're going to use both then apply the tape first. If you dope then wrap then I could foresee the tape being pushed out of the way before it gets gripped in the female threads.
Neither one is designed to produce a chemical bond, not sure where you got that idea from. These products aren't Loc-tite blue/red.
Both are designed to act as physical obstructions so that water cannot get through the threads. I don't think that using both hinders nor helps to stop leaks over using just one; proper material coverage and tightening are your best friends.
Some plumbers like to use both for whatever reason; old habits die hard I guess.
Maybe they've succumbed to some persistent inspector that likes to see both products applied so now it's a habit and propagated de facto. Here's an HVAC instructor that tells his class to &quot;apply mastic to the outside of flex duct to appease the inspector&quot;. Obviously this example is HVAC but the common denominator is the same; the inspector.
I have success regardless of which method I use.
I have a particularly rusted galvanized line to which I ran PEX. The threaded brass transition leaks a tear-drop every so often but it's actually caked with enough rust/hard water that it no longer leaks. I may try switching out the pipe dope for tape whenever I have some time to spare.