DxO are not specifically inaccurate, but like any lab testing the methodology is important to the interpretation of results.
The result as seen in files (used to obtain measurements) is a result of the WHOLE image processing chain, not merely one aspect. Every part of the image pathway is important to contributing to the accuracy of the capture process.
For example the lens affects those characteristics of light to a huge degree before you even get to the sensor which can be driven using different sensitivity settings, it outputs to various Op Amps (to raise/lower ISO) and an A/D converter which digitise what is (at that point) an Analogue signal.
All that is before you've even hit the Digital side of the image pathway, which while output is branded as raw, there is always some level of manipulation or encoding or interpretation when it is processed to see what the figures are.
Stop worrying about it, get the camera that does the things you want it to do, that you can afford and that you feel comfortable with.
TL;DR: Not only is it possible, it's LIKELY that two different make/models of camera have different characteristics.