Yes, we can fairly definitively say that inhabitants at Great Zimbabwe or in the surrounding realm of the same name would have had direct contact with Swahili traders as early as the 10th century. Well, technically someone in the 10th century would pre-date the foundation of Great Zimbabwe in the 11th century . We can say this because of the existence of trading settlements along the Zambezi valley from that period, and evidence of intensifying trade and growing integration of the Zimbawe plateau with Indian Ocean trade in the 11th and 12th centuries. The presence of beads and ceramics originating from Persia and India and dated to the first centuries of the second millenium found at sites in the Zimbabwe plateau is further evidence of this trade. ^1
It is also likely that a noble from Bonoman would have some awareness of the existence of Islam by the 14th century. Dyula merchants from from the Mali empire traded with Akan-speaking peoples for both gold and kola nuts. The city of Begho, located in the territory of Bonoman, is believed to have originated as a trade entrepot founded by these Muslim Dyula merchants.^2 ^3
As for the Kongoan royal of the 14th century, it is harder to be definite, but most likely the answer is no. If any sailors from the Indian ocean rounded the cape of good hope into the Atlantic before Diaz and Da Gama, there is no record of their voyage.
The example of Great Zimbabwe not-withstanding, otherwise there is not evidence of Swahili traders making their way far into the East African hinterland. For example, Swahili traders first reach the Buganda kingdom in the 19th century, spurred by the competition with European traders.^4 Since Mbanza Kongo was over a thousand miles away from the nearest considerable settlement of Muslim peoples, around Lake Chad or along the East African coast, it seems quite unlikely information about Islam reached Kongo by the 15th century.
the Zimbabwe Culture by Innocent Pikirayi, pp 92
Medieval Africa by Roland Oliver, pp 64.
The Archaeology of Islam in Sub-Saharan Africa by Timothy Insoll, pp. 334
ibid, pp 389.
Edit- fixed title. Edit 2- additional citation for Begho.