I would say yes, and if you are using a normal +5v regulator with a "straight through ground" you can hook the servo black/ground/- wire to the DEC- or you can use the ground on the output side of the regulator.
Do not try to "dim' an output to give you 5 volts.... don't even think about that... for an entire paragraph of reasons.
Greg
Okay, sage advice...….I ordered a six pack of the 5 volt regulators LM2596 DC to DC Buck Converted 3.0 - 40v to 1.5-35V Power Supply Step Down Module, the one shown in John's diagram in lower left corner, for $10.65 today.
The Massoth XLS Sound decoder installation instructions don't mention anything about having to use a 5 volt regulator to power a 5 volt servo like the Kadee #11220 Uncoupler in any of their information about using the decoder's A7 "Servo" connector. Maybe it's because the Massoth automatic uncoupler is a servo that uses 22 volts, so maybe Massoth didn't think about the need for guidance on using 5 volt servos which are the dominant type?