Navi, for what it's worth:
With regard to your examples (3) and (4), I have never heard anyone say "do scuba diving" before, and can find very few examples of it in print. I'm not saying it's incorrect, but it sounds awkward to me.
"Scuba dive" is certainly used often enough that I would say there is no question as to its acceptability, but I can find more instances of it being used as a noun phrase (as in "to perform a scuba dive") than a verb phrase. Furthermore, it doesn't seem to lend itself to the past tense; "scuba dived" is uncommon, and I can't find any examples at all of "scuba dove".
I prefer the phrase "go scuba diving", but I have no problem with your examples (1) and (2), which, as David said, are most naturally interpreted as (a).
Your example (9) got me thinking on a tangent, imagining the various interpretations it would take on if "not pilots" were omitted and "only" were inserted:
9a: Only sailors sing such songs in Spain.
9b: Sailors only sing such songs in Spain.
9c: Sailors sing only such songs in Spain.
9d: Sailors sing such songs only in Spain.
9e: Sailors sing such songs in Spain only.
No question here, just an observation.