They adopted rifle at least. Check out the photographs of Zulu warriors with what appear to be captured British rifles.

This South African military history details British guns of the Zulu war in detail, and mentions that there were instances that guns were taken without being disabled first, but without any mention of Zulu warriors using those larger weapons.

I've done historical reenacting on early 19th century naval cannon, essentially identical to the muzzle-loading cannon the British army had ~1870s. It takes a team of schooled, trained people to safely transport, load, aim and fire artillery. Any captured artillery would be far more complex than a rifle, and probably less likely to be used.