Is it legal for a roaming pokemon, IE mesprit, to have a Non-Event PID?
I'm not sure since they ARE encountered in the wild, and not in stationary events, however they are not like other wild pokemon.
Incidentally (and only slightly off-topic), I've only seen methods 1 - 4 as they are posted on that Smogon article by X-Act detailed out. Is the algorithm you just mentioned detailed anywhere?
My algorithm convention is better because its NOT confusing - The premise is simple:
Let there be 6 numbers, A, B, C, D, E, and F, where each one is a subsequent call to the RNG algorithm. Meaning A -> B -> C -> D -> E -> F.
Now the format is PID-Low, PID-High, IVs-High, IVs-Low, and for Method 1 (common for wild nds and gba pokes), its A-B-C-D, or ABCD.