Since every quad mesh is made up of triangles behind the scenes, every quad mesh can be converted to triangles by revealing those hidden edges.  There's ways to do that automatically in 3dsmax, for example.  Therefor, modelling in quads for low poly game development is common practice.

Instead of decimating quad meshes, I would prefer an option to reverse subdivision.  Yes, it's possible to reverse subdivision once it has been baked in too.

http://www.mariussilaghi.com/products/turboreverse

It's just a math algorithm after all.  So this wouldn't destroy UV's in most cases, and allow you to maintain quad topology, even for background characters.  Triangulation is good for game engines, but if you have to then smooth it again, as in the example on the Smith Micro websites, to get a nice secondary character, then it's ONLY useful in game engines.

With decimation, I would worry about bad results with IDL, and strange things in animation.  Reduction by stepping down in subd levels is a cleaner way to reduce polys for background characters, and maintaining UV's, decent bending in animation,  etc.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.