You need to do testing with the vacuum hot. Vacuum's output lots of heat and pet PIR's are designed to ignore objects of a certain size based on their heat output. The issue is the vacuum having the heat signature of a much larger object. Only real way to find out if your PIR's will be affected, would be to let the vacuum run and get hot. Near the end of the cycle, set your alarm and go stand under the PIR in the room (so it can't see you), then wait perfectly still and watch. Usually PIR's re-arm after 1-2 mins following a detection, so you should be able to leave the room, set the alarm, and return and position yourself under the PIR without triggering the alarm. From then on in, it's watching and waiting.
If the vacuum does trigger the alarm, then one option would be to re-position the PIR's in the rooms the vacuum goes in to detect above the height of the floor. Technically this opens your house up to burglars crawling around under the pir and undetected. That said, unless you're the Smithosian Museum, or something else with valuable treasures that attracts very sophisticated and planned thieves, it's unlikely your thieves will be crawling around or even thinking of it.