It all depends on your definition of swinging. If it's "both members of a couple get some strange on or about the same time" than no, hot-wifing is not swinging. But there are swingers who hot-wife and there are those who primarily hot-wife that swing. So there is a cross-over.
So though it's been posted before, I'll direct you to Franklin Veaux's excellent Venn diagram of non-monogamy http://tacit.livejournal.com/333842.html