Are review articles the result of original observations?
I think that review articles can of course be original work, provided that they offer something like an analysis of the current literature. A mere list of positions and the people who take them isn't going to count as a contribution to the literature. However, showing people that certain pieces of literature form families that have resemblences to one another, or that a certain piece has been cited a lot, although people have overlooked another important, but unknown piece that calls its thesis into question, etc. . .  those are all important, and indeed original contributions. 

I'm guessing that your article probably is analytical in this way, otherwise it wouldn't have been accepted for publication in the first place. I'd say that if it is a high-quality article, published somewhere respectable, then go on and include it in the thesis. Although obviously the usual caveats ("Check with your advisor!") apply.