Well... see service, depends on how one defines it
It saw service with "erprobungskommando" afail. Or a "test squadron" more or less flying most new plane types before final delivery to squadrons.
It is still not know wether any of the 30-35 (of which 14 were prototypes) A0's (pre-production) and A1's (first production version) saw any action.
Reports from Allied pilots said something similair to "A very strange looking plane but too fast to catch" being spotted, it is not know wether it was the Do 335 though.
Would be an awsome addition to AH but we will never see it I am afraid, not enough Data on the plane its service record.