There’s actually a small nugget of plausibility to this. See 46 CFR 11.301(g):
(g) Notwithstanding §11.901 of this part, each mariner found qualified to hold any of the following national officer endorsements will also be entitled to hold an STCW endorsement corresponding to the service or other limitations of the license or officer endorsements on the MMC. The vessels concerned are not subject to further obligation under STCW because of their special operating conditions as small vessels engaged in domestic, near-coastal voyages. [List of vessel types follows]
See also 46 CFR 15.1101(a)(2).
Anyone getting an STCW endorsement under 46 CFR 11.301(g) will have a limitation that is only valid for near-coastal domestic voyages, i.e. it’s not valid where STCW is required. As far as DPO, very few, if any, of the listed vessel types have DP.
For an STCW endorsement that’s valid where an STCW endorsement is required, see the regulation and policy I cited above.