Depends on what you mean by "successfully". I'd envision a resurgence of the insurgent breakaway movements in the region being an inevitable result, given that the Ovambo people launched several armed uprisings in the 1920s and 1930s, all of which were crushed militarily by the combined British and Portuguese forces IOTL. And it was in response to these uprisings that the South African administration continued to maintain the so-called "Police Zone", originally created by the Germans, which covered roughly the southern two-thirds of the province which later became Namibia, with the explicit purpose of confining and isolating the Ovambo in the north; Ovambo people were forbidden from moving into the Police Zone, but under these restrictions, implemented by the British in 1936, neither other tribes nor Europeans were allowed to move north into the designated 'Ovamboland' region without permits either. Because of labor shortages in the Police Zone and South Africa, exacerbated by the native Africans' struggles to recover from atrocities such as the Herero and Namaqua genocide, the South African government elected to allow migrant wage labor, and permit the Ovambo migrant laborers to move back into the "Police Zone", as well as to other parts of SA (albeit with strictly imposed segregation and diminished human rights), with the Urban Areas Act of 1923- however, few Ovambo did, preferring to stay in their homeland and continue fighting for their freedom.
So then, SWAPO, or some variant of it, definitely isn't getting butterflied away- if anything, given that the Portuguese'd most likely be far weaker, militarily, manpower and force-projection wise, than the British and South Africans were, the Ovambo peoples' armed uprisings in the 1920s and 30s would've likely been far stronger and more effective than they were IOTL, and would've had a far greater chance of succeeding far, far earlier ITTL than they did IOTL, better than 50-50 IMHO. One with the potential to even liberate Ovamboland (i.e, not just the greatly reduced Bantustan of Ovamboland, which was created by the SA as part of their Odendall Plan, but perhaps even historical Ovamboland in its entirety, depending upon how far south and how far inland the new border of Portuguese Angola goes), by the early to mid 1930s, prior to the outbreak of WW2.
And with a third, newly independent African nation in addition to Ethiopia and Liberia added to the mix during this time period- one established through a native African military rebel movement successfully ousting the white colonial authorities from the region, predominantly comprised of formerly German Imperial territory, right on the North West border of the Union of South Africa? One can only imagine how much of a geopolitical impact that might've had...
