While you may have established reasonable confidence in the Lenovo Power Adapter supporting USB-PD, despite lacking explicit markings that would provide confirmation, you do so entirely at your own risk.
Personally, I’m not prepared to recommend using any Power Adapter that does not carry appropriate markings or type-certification. There are proprietary charging standards that appear very similar, but are not USB Power Delivery compliant. Other contributors may be less risk averse - but then, perhaps they can afford potentially damaging consequences of a failed experiment.
Perhaps consider that consequential damage to your iPad will not be covered by either your Apple device warranty, or any warranty that might exist with the Lenovo Power Adapter. The cost of a known compatible Power Adapter, of adequate power output, pales into insignificance when compared with the cost of potential repair or replacement of a damaged iPad, or for that matter your Belkin dock and other connected devices.
In summary, it’s entirely your choice and risk to take.
Would I? No.