Can identical DC power supplies with common ground produce varying voltage on same circuit?
As the power supply is a low impedance source: even small differences in voltage output can result in large currents flowing between them if the supplies are connected in parallel. Depending on the design of the supply this may cause damage.

Rather than connecting the supplies as shown it would be better to connect the power and ground at the strip for each auxiliary supply. This will keep the ground current in the common ground within sensible limits and as the power ground is also used as a signal ground will keep the ground noise down for signalling.