No reason for that, you're going to turn them round anyway.
If you're concerned about getting the tube in the center of the blank, you just need to have enough wood around the blank for turning. Exact center only matters with special segmented blanks and similar.
You don't want to run any small things like a pen blank over a jointer. The length is too short to safely bridge the gap over the cutter between the two tables. If longer (10' or more) it is safe but you can only get the sides adjacent to one corner square before needing a thickness planer to make the other two sides parallel to the first ones. In this area 6" jointers come up on Craigslist for the same money and less quite regularly. Occasionally there are 4" ones for sale too if space is your issue.
Thanks for the feedback! I would be using it for segmenting and Celtic knot pens. I do have a planer and would be starting with blanks of wood larger than the finished blank.
Don't waste your money. First off they are not stable. Need to be anchored. I make lots of knots and segmented blanks and have never used a jointer to make any one of them. A good tablesaw is a good tool to have and can do so many different functions of woodworking. That is where i would spend my money.