Nobody can tell you for sure whether he will be allowed to interview in Sweden. That is not a USCIS decision. Approved I-130 decisions are sent to the National Visa Center, but it's up to the Immigrant Visa unit in Sweden whether they will allow him to interview there.
No, his status in Sweden does not impact either the petition approval or the visa beyond whether he will be allowed to interview in Sweden.
With all that in mind, the decision to marry is a weighty one indeed.