You can. I have a NVLT5 that has been running about 5400 for a couple of years (following a minor upgrade) and it will go on up above 5500 iirc. Now... Just because it will, doesn't mean that you should.
I would highly recommend going with the next larger step TX or add another bay to the antenna or increase the feed line size, etc to keep from running the tx wide open.
If you do run it at 5500, be very diligent in keeping the air cool and clean and make sure that the antenna is tuned properly.