I don't think anyone's really studied kratom digestion. It's a whole leaf, so there'll be a lot of compounds passing through.
The main ingredient is mitragynine (and derivatives), and the closest studied drug, structurally, is yohimbine. That drug has "rapid absorption" but low availability and high variability. I don't know if that means it's absorbed through stomach lining; if you have rapid gastric emptying without a pyloric sphincter, that might affect your ability to absorb the active compounds. And without a sphincter I don't know how you could delay that--if you're diabetic you just eat some protein and it'll gum everything up while your stomach works on it, before moving on the duodenum. But that requires a sphincter.
It could, of course, be absorbed somewhere else, and sliding through your stomach just speeds it up more. Too many confounding compounds and unknowns. I'm afraid to check if we have a plugging kratom thread, but we probably do.