Although the token is attacking, it was never declared as an attacking creature
However, instead of caring about spells cast before it was, Gravestorm cares about the number of permanents put into graveyards this turn
While Rest in Peace is on the battlefield, abilities that trigger whenever a creature dies won't trigger because cards and tokens are never put into a player's graveyard
However, I find they aren't really lands, so they're more likely to get targeted or blown out by stuff like Vandalblast
It's honestly no surprise that the three most valuable Medallions found herein are in Grixis colors, as those are the ones in which storming off is the most appealing (and satisfying) way of ending a game of Magic
Should We Worry About the Pinkertons