In theory you can use MultiChain for a cryptocurrency, but if you're using open block mining, this means your chain will be secured by proof-of-work. You should be aware that MultiChain uses the same proof-of-work scheme as the bitcoin network, so a small proportion of the bitcoin mining power can be used to attack your chain.
As for an API to connect to a MultiChain network, I'm not sure what you're asking, because you could create your own API for your network if you wish.
