>Ketchum sounds similar to catch 'em. First name can be found in Japanese name, S a to sh i. Also, Ash is a default name for Red in Pokémon Red and Blue. Ash trees are suggested as another explanation as well.
So, as Bulbapedia suggests here, you're absolutely right!
Also,
Pikachu has a special fondness for ketchup
as shown here, so that might be a play on words, showing that Pikachu likes Ash so much too.
Image credits: Bulbapedia
