A friend of mine stated that this can't be a Standard American Lager, due to the use of Munich & Bohemian Lager yeast.
Is this true?
Like Denny says, if it tastes like an American lager, it is.
That said, your beer might not be a Standard
American lager according to the BJCP guidelines. The Bohemian lager yeast might give it a slight hint of diacetyl, the Munich malt might make it too dark and too chewy for the style, and the hop aroma and bitterness might be a bit too pronounced. Looking at the guidelines, you'll notice that the commercial examples for SAL include things like PBR and Coors Original.
If you were to enter in competition, the closest category for it might be Dark American Lager (4A), although it actually sounds more like a "Pre-Pro Amber American Lager" along the lines of Sam Adams Boston Lager or Brooklyn Lager.