You don't need to upgrade BUT you should save your SHSH Blobs for 4.3.3 now. See the sticky on how to do it. This allows you to upgrade to 4.3.3 if you are at a lower version regardless of whether Apple immediately release a 4.3.4 and stops signing 4.3.3, which you can be fairly sure they WILL do as soon as the JB is released...
However, this advice is good for the WiFi only iPad2.
If you have a 3G / CDMA iPad2, then you may need to think more carefully. We know that without a successful baseband install, the iPad2 update will fail and cannot be recovered, necessitating a restore to the latest version. So you cannot use SHSH Blobs to upgrade / downgrade a 3G / CDMA device.
The best advice I can give is to wait until the JB is released and make a judgement call. Apple never close the signing window immediately. So, IF the JB is for 4.3.3 you can choose to upgrade to 4.3.3 and THEN Jailbreak. If you do it within a day or two there is no way Apple will have released a fix and stopped signing...
Hope that helps.