Yes, you can absolutely use kratom between doses of an opioid. I do this regularly and have been for 6 years or so.
What I have found in my numerous trials (seriously hundreds if not more) is that a full dose of kratom and a full dose of an opioid like hydrocodone or oxycodone leads to somewhat diminished effects and it is not as good as either substance alone.
However, I have found that a lower dose of kratom combines rather well with hydrocodone or oxycodone. Also, because I am completely physiologically addicted to kratom (daily habit for 5 years, at least an ounce a day, usually closer to two ounces per day) I have to take a large dose in the evening and I have found that I still experience withdrawl symptoms if I take only hydrocodone or oxycodone and no kratom unless the hydro or oxy dose is higher (like 40-60mg).
Every night I take ~15 grams of red bali and 3 hours later ingest 10-30mg of hydrocodone and find this works rather well to extend and enhance the painkilling effects.
As always, know your tolerance and your dose. Most importantly, be safe! That is my experience with combing kratom and prescription opioids. There are quite a few threads on this topic and many people state that they do not find the combo rather enjoyable.