My company also pays out an annual bonus in March. They explicitly state that you're eligible for the bonus if you're on the payroll as of 12/31. I've had co-workers leave in early January, and I assume they got the bonus, although I never checked with them. I have no idea if this is standard, but you may want to check.

(Not sure how you can ask your company's HR about this discreetly, though...)

This is correct - both companies I've worked at that had revenue bonuses paid them out only to people employed on the day the bonus was issued. New people who weren't around for the entire fiscal year got the pro rata bonuses.