I think is partly semantics. If you want to stay on line and via timing or sen no sen beat the other person to the strike then that's one thing but it's not irimi. The word itself is to do with passing or passing behind in fact..
Not really. Though I don't have my Japanese wordprocessor here to input the kanji, "irimi" is a compund of the verb "iru" to enter and "mi" or body.
It doesn't necessarily mean passing or passing behind. Not at all.