It might or might not be perfectly normal for freehubs to wobble based on their particular design. Also for this purpose, I'm defining wobble as side to side, or up and down movement most visible when the hub spins while the freehub is stationary.

basically we can divide freehub designs into two classes.

1- those mounted directly on the axle with their own bearings and connected to the wheel hub only through the clutch (ratchet) mechanism such as the Campagnolo system These run true because they are independent of the hub itself, and do not turn when not pedaling.

2- self contained freehubs with internal clutch and fixed to the hub shell via spline or thread, such as most Shimano freehubs. With these, ome wobble is normal because the axis of the freehub rotates with the wheel so even though the cassette is stationary it's axis isn't, and any mis-alignment at the mounting point will cause wobble in a way similar way that a bent crank will cause the pedal to oscillate underfoot. Wobble within the normal range is no problem, though many are surprised when they first notice it. Older riders used to freewheels are used to seeing and accepting it.

If the wobble is slight, I wouldn't sweat it, if it's significant on a design of the second type it might mean that the freehub/hub interface is loose, or damaged to the point of imminent failure. It's a judgment call, based on knowing what normal runout looks like. You might also want to double check that the connection to the shell is tight.