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".
Normally I wouldn't be this pedantic, but in a discussion about currency, it's worthwhile specifying whether you mean American dollars, $some_other_country's dollars, or the Platonic form of dollars.
I meant US dollars, but now that I think of it, you can do transactions in any currency using Visa, which is more evidence that they're a payment system rather than a competing currency like "visabucks" or something.
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.