You're coming at this from the wrong angle. While you're correct about the rhyming, the implication for the name lies only in pattern recognition. Take the sign literally and the store could've been called either "Chuck's" or "Chuck's Feed and Seed". The implication of "Chuck's Fuck and Suck" comes only from seeing the rhyming pattern.
Yes, that joke was the intended effect. But it's on viewers to recognize the pattern and think "what the hell, did they really…?" or whatever. Taken at literal face value, the sign is perfectly innocuous. If anything, the joke is on viewers who see the sign, do some RegEx work in their heads, and get an adolescent giggle out of the end result.