Nippon Sharyo made DMUs for SMART train service north of San Francisco, and for UP Express train service in Toronto. They closed their USA plant, so any future DMUs built by them will probably be built in Japan, and would not qualify for federal funding because they are not Built in America.
That leaves just Stadler DMU trains, GTWs and FLIRTs. GTWs are not built in America - but FLIRTs are in Salt Lake City. Riverline, CapMetro Rail, DCTA, and eBART are using DMU GTWs today. Presently, TEXRail is the only service using DMU FLIRT trains in America.
DART has ordered more DMU FLIRTs and will have them in service soon.
When proposing new DMU train services, do not forget that tracks without Positive Train Controls owned by non Class A railroads are limited to 6 round trips a day for passenger services (12 trains a day). There are other requirements that must be met as well, such as no hazardous cargo and low cargo tonnage. Otherwise, a new passenger service will have to have expensive PTC systems installed on all the trains and tracks to be used.