Certainly, for example i believe both sides used trenches as part of the siege works around Mafeking (one of the engagements Baden-Powell the creator of The Scouts was involved in as a little side note) and Kimberley for example. In these cases it was relatively early in the war when the Boers were taking a more direct conventional approach they attempted to take some of the British towns along the boarder between the more central territories of the south African republic and Cape Colony. In both British defenders dug trench networks around the outer edges of the towns to defend them. Storming these defensive positions would have been risky and costly so the Boers shelled the towns, harassed the garrison with skirmishers and dug their own trenches and made sangers around and on the hills above the town as part of the sieges until both towns were eventually relived by reinforcements from britain. The siege of Ladysmith was similar with british forces digging sangers type positions on the hills around the town to defend it and the Boers encircled them, while i image they did i'm not certain if the Boers dug their own opposing trenches.

Trenches in general would continue to be used by both sides when ever defending a static position was needed and there was time to dig them though as the war went onward and there are plenty of other examples that i don't want to get too deep into or else i'll be here all day like Spionkop when the Boers entrenched the top of Spionkop hill british troops managed to make it part way up the hill in a night attack but hadn't the time to dig in deep enough for their trenches to provide sufficient cover from the boer artillery higher on the hill which had a good angle on them.

But in general its something of a misconception that trenches were actually new in the first world war. They had been used in siege warfare in particular for centuries though their importance had arguably been steadily increasing over the course of the 19th century as the effectiveness of artillery and infantry fire increased, necessitating increased use of trenches to protect troops and increasing the defensive fire power of infantry. But this cumulated on the western front with trench warfare becoming so dominant that there was an unbroken line from sea to Switzerland given firstly that the increased use of machine guns (Which were used in the boer war by british troops but weren't yet produced on the same scale as they would be by the end of the war) and barbed wire helped to further augment the defensive capabilities of infantry while indirect artillery fire was becoming predominant and increasingly powerful necessitating these kinds of defences to an even greater extent. Meanwhile the scale of the war with how many troops and industrialised nation was now able to equip in a large conventional war meant that they were able to form an unbroken defensive line along the entirety of a front of that length.

The Boers did use trenches, but it was far from the earliest use of trenches. Trenches had already seen use in the Musket Wars in New Zealand as early as the 1820s, the Crimean War, and the American Civil War. The other key ingredient of WWI trench war - barbed wire, which made the killing ground of No Man's Land much deadlier - was first used on a large scale in war in the Russo-Japanese War of 1904-5 (together with trenches). Trenches also saw much earlier use in sieges in Early Modern warfare - the firepower of a typical trace italienne fortress (AKA star fort AKA artillery fortress) forced the attackers to dig trenches to get closer to the walls once within range.

The value of cover from enemy fire, including on the battlefield as well as in siege, had long been appreciated. Thus, the common use of mantlets and pavises. These have a major advantage over trenches: portability. They can be redeployed if the enemy moves elsewhere, or attacks from an unexpected direction, etc. Trenches, OTOH, are immobile (a far lesser problem in sieges, accounting for the much earlier common use of trenches in siege warfare). The appearance of handguns and cannons that could shoot through mantlets and pavises made them far less useful, and stouter cover was needed. Trenches were one option, but other types of protection such as earth ditch-and-wall fortifications, gabions (baskets filled with earth and/or rocks) and timber-and-earth walls were also used. Such above-ground protection is usefully a greater obstacle to attacking infantry than a trench - infantry can jump into a trench more easily than they can climb out of a ditch and over a wall. Once explosive artillery shells are in common use, the front-and-back protection of a trench can make it much better than the front-only protection of an earth wall. For example, the Maori response to muskets consisted not only of trenches, but also earth walls and thicker wooden palisades. With war between Maori and the British in the 1840s, with heavy British use of artillery, including howitzers, mortars, and Congreve rockets, trenches became essential.

The relatively late common use of trenches outside sieges is understandable. Using smoothbore muskets (or crossbows), a charging enemy can cross the zone where the defenders firepower is effective very quickly, and the defending troops can only reliable depend on getting a single shot against a charging enemy. This, combined with the immobility of trenches, makes them much less attractive. Once rifled muskets became common, the greater effective range made trenches more effective; with breech-loading rifles, magazine-fed rifles, and barbed wire to impede attacking enemy infantry trying to reach the trenches, trenches became even more effective.