A PKM file is just a file (similar to a Word document or picture file like .jpeg) that contains the data/information of a Pokemon. Yes the Arceus would be able to unlock the events in Platinum and HeartGold/SoulSilver, and it would have the OT TRU. However I think for the Regis in Platinum you have to use the Regigigas. Also the use of PKM files isn't hacking.
I have the following Lonely Nature TRU Arceus (none on my Pearl version):
Strongly Defiant - Nov 9, 2009
Loves to Eat - Nov 8, 2009
Good Perseverance - Nov 7, 2009
Mischievous - Nov 15, 2009
Somewhat Vain - Nov 14, 2009
Strongly Defiant - Nov 13, 2009
Often Dozes Off - Nov 12, 2009
Likes to Run - Nov 11, 2009
Likes to Run - Nov 10, 2009
What TRU Arceus with a Lonely Nature are you interested in?