Both Wonder Girl and Harvest allow you to start the game with them assigned a relic that doesn't impac your object total. Does this still make it so that you cannot have a resource assigned to your force?

Just asking now because my point total for a team im working on could fit both, but if I can only have one then the belt is going to beat the lasso every time

That's what it means. While the relic doesn't count towards your object total, it is still a part of your force and will prevent you from assigning a resource.