Yes its possible to have success in online poker without using a HUD. Some sites dont allow them, and then the choise gives itself. However if you choose to play on a site, which does allow them, then you are putting yourself at a disadvantage to those people, who know how to use a HUD well. And you are also missing out on the great tool, which a tracker is for working on your game away from the table.
So you might want to change your mind at some point and invest in a good tracker like PT4. For me this program is the best value for money, you will find anywhere inside the world of paid poker software and/or training. It also makes it easier to use other software like ICMizer, because you have an easy way of mass importing hands for analysis.