I agree, having the guideline be to simply include a certain Pokemon doesn't really do much. In the SPPF contest which I wrote for, the condition was to feature a battle with a Cacnea against a Sandshrew, as well as an evolution (which doesn't necessarily have to be either of the aforementioned battling Pokemon). Not only did I lose that, but I didn't even get in the top ****in' three!!! While I couldn't say the one-shot I wrote was perfect, especially that early draft (incidentally, this is the very same one-shot that eventually evolved into my hentai), I at least stuck close to the subject matter at hand.
My story was a romance taking place in a desert, with a Cacnea as the main character's Pokemon. Early on, he battles against a cheeky kid with a Sandshrew, and ends up losing when it evolves into a Sandslash mid-battle (and said battle was kind of important). You know what the first-place winner was? Some story about a Fakemon that escapes human captivity and evolves in the process (or something like that), and where was the battle between a Cacnea and a Sandshrew? Briefly mentioned to be occurring in the background, that's where. Seriously, how the bloody hell do I lose against a writer who just passes most of the given subject off into a side-note? [cough] But my personal venting aside, a writing contest should actually expect the writers to heavily involve a certain subject in there story, not just plop it into the background and be done with it. If writers can't really show how they can deal with certain restrictions, a particular element they're required to involve in their work, then what's the damn point? You may as well just have a typical "who can write the best one-shot?" and not even bother with specific themes.