Most of the time. But sometimes, no. See ATL thunk emulation (last I checked, still alive in the windows kernel) and ntvdm handling of the BOP pseudoinstruction.

See also: Jazelle DBX.

Hell, on modern x86 processors, many “native” instructions are actually a series of micro-ops for a mostly undocumented and mostly poorly understood microcode architecture that differs from the natively documented instruction set.

It’s turtles all the way down.