Independent is often used as a weasel word ie: independent franchises. So sure the could be an independent distributor or whatever but that’s not actually independent as they would have a financial connection.
Remaining objective is of course possible even with financial ties, but the suspicion is going to taint people’s perception.
If ifixit were to partner with a manufacturer (and especially one as large and influential as Apple), there might be a perception among consumers (whether true or not) that they were beholden to the manufacturer not to do anything that might hurt that manufacturer's revenue streams, like (for example) providing parts and information to extend the use of obsolete products or criticizing any of the manufacturer's design practices that might be hostile to repair.
On the flip side, it might be possible for a partnership to provide better first-party parts support and more complete sharing of information, but I'm just too jaded to believe it could happen that way.
Remaining objective is of course possible even with financial ties, but the suspicion is going to taint people’s perception.