Why can this not be "Do you like going swimming?" which I interpreted it as due to the presence of gehen? Alternatively, could I ask "Do you like swimming?" by saying "Schwimmst du gern?" in German?
The first sentence should be an acceptable alternative. Sometimes newly-added sentences are missing alternatives, and you can help by reporting them during the lesson.
The answer to your second question is "yes".
Do you like to go swimming? Are there other verbs where you can add GEHEN like this. Gehst du gern wandern? Gehst du gern laufen/rennen?
Is this example sentence unique?
My point is same as Nick's below
Gehst du gern Schwimmen. Literally means. Do you like going(gehst) to swim. Why wasn't my respond accepted???