Cat 6 PoE Parallel To Power Cables (just for 2 feet) - What should I expect?
Sorry, but I don't think you are allowed to do this. See Cat 5/6 in same conduit as power: is NM-B required, or is THHN acceptable? for more information.

So while there may or may not be any actual technical problem, there is a code problem. Would there be a problem running your Ethernet outside the conduit, just inches away? According to code, no problem at all (as far as I know). Would it cause any technical (signal quality) problems? My guess is probably not, especially for just a few feet.

But you can't run it inside the same conduit. You can (and this is a frequent suggestion when pouring concrete or digging a trench) run multiple conduits and have a small one for network/phone/etc. and a large one for power. But you can't just throw everything into one conduit.