either way, the weight of the fan blade assembly is not resting on any bearing when oriented to blow upwards according to the engineering drawings of various bearing types I've had the chance to find. there MAY be a fan out there where the fan blade assembly is actually resting on a bearing of some sort (instead of the retaining clip) but I haven't found the brand/model for them yet. like i said. when blowing downwards, the central axle is actually resting on a ball bearing, but when blowing upwards, it's just resting on the retaining clip.
i would LOVE to find and recommend a fan that is actually engineered to blow air upwards since most of the fans in use for modern builds have the need to blow upwards for 1 reason or another.