It MAY work on DC.
In my experience only "vibration motors" need AC. And what they really need is the 0v point between shifting from pos. to neg.. DC does not have that, the power is a constant, more a line than a wave when seen on a graph. Half wave does have 0v though (basically a pulsed DC by using only half of the AC waves.)
I’m assuming that it doesn't use the postwar vibration motor, but a small can motor. That means it most likely changes to DC internally anyhow. Not to mention any controller board having more than resistors or capacitors would need DC too.
Most AC motors run fine on dc, especially if not in constant run mode. It's running a DC motor on ac without rectification to DC that you'd end up cooking a DC motor (Sometimes running on DC can effect an ac motors heat range in a constant on mode as some may rely on that 0v point for cooling. Early Williams can motor test prototypes would run hot as heck on straight DC because the dc motor wasn't really designed for long term continuous operation. It was designed for short bursts of use. Half wave worked better for cooling reasons, but was a little "lumpy" or jerky on slow starts. I'm not actually sure what went into production; but the example is for decription more than accuracy on what's out there in use.)
It is highly unlikely that testing with DC could do harm. It either will work or won't on dc.
If it doesn't work on DC , It's more likely the BOARD uses the POS&NEG ac waves seprately for different things on the board, but I've only seen that on a single Weaver loco for sounds, nowhere else in trains have I heard of it... Yet