Yes, they could, but as you note it required certain property and other qualifications. This was the Cape Qualified Franchise or Cape Limited Franchise, which was a holdover from the agreements that created local colonial governance and a parliament in the Cape Colony (1853) and the beliefs of the Cape Liberals of the mid-late 19th century about the Christianization and 'civilization' of Africans to European standards being a process that conferred such rewards along the way. This franchise, for those few hundred to thousand who qualified, then was preserved in the Cape Province under the South Africa Act (Union, took effect 1910). Its preservation was connected to the case Thomson and Stilwell v Kama and specifically its appeal (1917) which determined that the provisions of the 1913 Natives Land Act, which would have denied Africans the right in the Cape to own land outside of certain circumscribed areas and modes, would constitute an unacceptable disenfranchisement. In practice, they could make it harder (financially) for Black purchase of lands but they could not wipe it out because of that franchise, and the franchise itself had a high bar to clear to be eliminated outright. It is worth pointing out that these voters were only ever a small percentage of the country overall, and their representation in the House of Assembly was always white and only a few percent of the total body.

This Cape franchise was eliminated for Black voters generally with the Native Trust and Land Act of 1936, one of JBM Herzog's 'Native Bills,' which 'traded' those rights for an expanded schedule of released areas in which people could own land. Their voting rights in the Union at large were then converted into the rights that other Africans enjoyed, namely only those over local councils and district bodies governing their areas specifically--not national ones. This was a key segregationist moment, and later apartheid measures would use many of these boundaries as starting points for things like Group Areas. Again, there was enough disagreement even under the United government to prevent the simple rescinding of this franchise--because it involved the more-liberal Cape province's provincial rights.

In Natal, there were only a few Black voters (the last I think was the 1948 example whom I've not yet been able to suss out) under a system I don't entirely understand but may have been tied to the missions, while in the Free State and Transvaal the franchise was denied them wholly (although there were initially one or two people 'granted' the right of burghers in the old Republics, in another weird exception well before 1900). Ironically, it seems that transfers of land to trust or to Black ownership increased after 1913, approved by Union government on a per-case basis under the law (outside the Cape), but such ownership did not suddenly create large new bodies of voters even though whites were constantly concerned about this kind of thing in a sort of paranoia. Harvey Feinberg and Johan Bergh have talked about this land issue in articles, most appearing in the journal Historia, and it seems counter-intuitive but the land transfers are clear. Section 12.2 in the fifth edition of Davenport and Saunders' South Africa: A Modern History covers response (to the 1936 bills), and although it's older it has a decent bibliography to start from.

Please note that this isn't the Coloured franchise, which is something different, eliminated in the late 1950s for most purposes; nor is it the Indian franchise. This is specifically for Black (or African) South Africans, who would later face denationalization under apartheid.

I will update and edit if needed when I have access to my full bibliography, including theses and other works. Apologies if I've forgotten any of the steps!

[edit: It's worth noting that the major Cape legislation for individual title to land, the Glen Grey Act of 1894 and its extensions into the Transkei, specifically stipulated that the land so titled was not considered as qualifying for the franchise--lest many new thousands of Black voters appear on the rolls! But many did own or obtain land under freehold title in the standard way, under market provisions, or in older subdivisions of lots; those were the Qualified Franchise voters.]