Duty cycle limitation is applied to transmission, not reception
Yes. An 8-channel gateway is actually rather complex, it can receive on 8 different frequencies, it can theoretically actually receive two signals at different spreading factors on the same frequency at the same time.
At some stages of the receive process there are a number of dynamically assigned “engines” which can work the problem, and if they are all assigned chasing other possibilities (even false ones), a possibly valid signal might not be investigated.
Having a node extremely close to a gateway can actually increase the chances of this, because strong signals can weakly bleed over and appear as weak (possibly unintelligible) false signals on other channels. This could increase the number of distractions the gateway chip’s processing engines have to contend with in finding the valid signals.