For On the Road, he wrote as his thoughts came to him, and the original manuscript had no form and no real syntax. He just wrote in a sort of stream-of-consciousness way, and the story wasn't tailored or refined at all but just a scroll of text, really. I doubt an INFP would accept that. Ne would kick in and we'd start picking apart how exactly we could reach a more perfect idea of whatever our idea is (disillusioned with the reality of what we've created - doesn't match the dream), if that makes any sense. We tend to have some perfectionist tendencies when it comes to something we care about or believe in, and we tend to be overly analytical about those things, sometimes to a fault. Also, much of Road is autobiographical, thus I doubt too that an INFP would be hopping from Colorado to San Fran to Mexico and back just for the thrill of it, or to salve his loneliness. I've seen that more in ISFPs, even ESFPs, I know: they use a change in scenery and material things or more sensory, more external sources to resolve whatever emotional issues they're engaged in. I can't really see that happening for the more "cerebral" INFP, which is probably why we have a reputation for being the "brooding" type.
Frankly, I don't know what Kerouac believes in, and I think I'd get some indication of that from FiNe but not necessarily FiSe.
Whitman, however, could go both ways. It's just that I've always seen him as FiSe. I can't explain why, but if I come up with a better reason than "I just feel like that's right" I'll come back.