For John Robert Colombo, I would definitely say that the form supports the tone. Limericks, almost by definition, contain a pun or humorous twist at the end of the poem. They are light-hearted and humorous. A reader, simply knowing the poem is a limerick, expects the poem to be accessible and fun to read. Colombo's limericks are exactly that. They are not difficult to understand, and they contain humorous twists within them.
"A poet from Winnipeg, Man.,
Wrote verses that never would scan,
When asked why this was
He replied, “Well, because
I always try to fit in as many words to a line as I can.”
This poem is a good example of Colombo making fun of himself. He's a Canadian author, so the opening line marks the poem about himself. He then admits that some of his poems don't always scan poetically correct. Then the last line just gives up on trying to stick with the correct syllable count.
John Whyte's "I've Always Lived Across the Street," on the other hand, is written in free verse. The tone of the poem is light and humorous. That's right in line with Colombo's limericks. However, the structure of the poem does not alert the reader that it will be a humorous poem. Most free verse poetry is more serious. Free verse is more of what English teachers might call "deep." For example, Walt Whitman wrote a lot of poetry in free verse, but it is rarely humorous. Langston Hughes's "I, Too, Sing America" is about racism. No, Whyte's use of free verse does not alert the reader to a light tone.