Maybe! An essential element of designing contracts is figuring out exactly who's taking what risk. From what the freelancer says, it sounds like Upwork is saying, "If you track the time directly with our tool, we'll take the risk of fraud. But if you track time your own way, the risk is on you." I assume that's what the guy actually agreed to, as he didn't say otherwise. So in this case, it sounds like it's something UpWork isn't taking a share of revenue for.