I believe (and I'm far from the only one) that kratom blocks or occupies the opiate receptors for a significant period of time after the last dose. 2 - 10 days seems to be the time range different people are experiencing and reporting.
Taking weaker opiates like codeine or even DHC is completely pointless during this period, as all good effects will be blocked.
However, after this period, I don't think that even the best kratom would have much effect on tolerance of relatively strong opiates like oxycodone.
7OH is a different matter, as I gather that it's 1000 times stronger than 'normal' kratom, so that may well affect opiate tolerance.
Although the mechanisms of action and receptor agonism will not be the same, so it might be comparable to alcohol consumption not really affecting benzo tolerance, AFAIK, although they both act on GABA A receptors.
tl;dr I don't know for sure, but probably not a massive effect on tolerance, once the opiate receptors are no longer blocked by the last dose of kratom.
