No, they are not currencies, they are payment methods for dollars. A note that you owe someone some amount of dollars is entirely different from saying, repeatedly, in advertisements, that you're an "alternative currency".
The principle here is that you're not allowed to compete with the US gov't when it comes to providing the currency of the land. There are a lot of good reasons for this, and some mediocre reasons to oppose it, but at the end of the day it's pretty clear that there's a difference between Liberty Dollars and a cashier's check denoted in US dollars.