nah it seems like they just added it so english speakers would know to pronounce the e at all, ie it's not "poke mon". in japanese it's not a problem because they'd pronounce the e regardless.
guess i'm not sure why they'd put "poke'mon" in the first place. usually apostrophes like that are used to indicate stress, and in english the stress in pokémon is on the first syllable. basically they did the é for the same reason some people write "animé" -- to show dumb english speakers that you're supposed to pronounce the e. i don't think it was some haphazard decision.
guess i'm not sure why they'd put "poke'mon" in the first place. usually apostrophes like that are used to indicate stress, and in english the stress in pokémon is on the first syllable. basically they did the é for the same reason some people write "animé" -- to show dumb english speakers that you're supposed to pronounce the e. i don't think it was some haphazard decision.