I've read a comment somewhere saying that there was no evidence that greatswords were used to disrupt pike formations and that got me thinking:

-Is this comment true?

It's true, or at least very close to true. There is some ambiguous artistic evidence that it interpreted as greatswords being used to attack pike formations. Two of the most-cited artworks are:

• Battle of Kappel woodcut: https://commons.wikimedia.org/wiki/File:Schlacht_bei_Kappel.jpg

• Battle of Pavia tapestry: https://commons.wikimedia.org/wiki/File:Battle_of_Pavia.jpg

On the left of the Pavia tapestry, a soldier with a greatsword is fighting pikemen. However, it is just a few pikemen, apparently out of formation. The group of soldiers in the middle of the Kappel woodcut are fighting the enemy pikemen, but it isn't clear that they're being used to disrupt the pike formation. First, no friendly soldiers are ready to exploit any disruption if they succeed. Second, it can be explained as the swordsmen are attempted to cover the retreat of their fellow soldiers to the left of the woodcut; this better matches literature on the use of greatswords.

-Would they do anything outside this specific situation?

Their main use on the battlefield, as described in texts, was for guarding standard bearers and officers. This takes advantage of one of the strengths of such large swords: they can be used to control a lot of space. For example, two soldiers with greatswords can control a space 8-10m wide (25-30 feet), and stop enemy from reaching the standard bearer or officer. While they won't be able to hold off the enemy indefinitely, and will have trouble with enemies with pikes and other long polearms, they will (hopefully) hold them off for long enough for help to arrive.

For example, the Trewer Rath und Bedencken eines Alten wol versuchten und Erfahrenen Kriegsmans (True Advice and Reflections of an Old Well-tested and Experienced Warrior) of about 1522, possibly written by the Lansknecht commander Georg von Frundsberg, places

Führern, Furirern, Waybeln und Schlachtschwerter

with the two standard-bearers in the middle ranks of the formation (and the front 4 ranks are Doppelsöldner (double-pay soldiers, usually well-equipped veterans) and the captain, the last 2 ranks more Doppelsöldner and the lieutenant). "Schlachtschwerter" is literally "battle swords", and refers to the large greatswords of the time (AKA Zweihänder). Similar, John Smythe, in his Certain Discourses Concerning Formes And Effects Of Weapons of 1590, noted that

the great Princes of Germanie ... form their regiments of footmen into great bands of 500 to an Ensigne ... their milicia consisting of Harquebuziers, Piquers, and some Halbarders, with a few slath swords for the gard of their Ensignes

where "slath sword" is the English version of Schlachtschwert ("slaughter sword" is also used in English).

In his fightbook Ragione di adoprar sicuramente l'Arme of 1570, Giacomo di Grassi explicitly discusses the value of the greatsword for one-against-many, and notes its use for guarding standard bearers on the battlefield:

But because one may with it (as a galleon among many galleys) resist many Swords, or other weapons: Therefore in the wars, it is used to be place near unto the Ensign or Ancient, for the defense thereof, because, being of itself able to contend with many, it may the better safeguard the same. And it is accustomed to be carried in the City, as well by night as by day, when it so chances that a few are constrained to withstand a great many.

and also its use by city guards.

For the same reason, greatswords were used to cover the flanks of pike units - the Scottish army at the Battle of Flodden (1513) adopted the "German style" of battle, and deployed them in this way.

Two further points can be usefully made. First, Doppelsöldner were mentioned above. It is sometimes assumed that Doppelsöldner usually used large greatswords, and large greatswords were usually carried by Doppelsöldner. Most Doppelsöldner were armoured pikemen (thus, their deployment in the front ranks, and also in the rear, to keep the formation steady). Trewer Rath notes that "Doppelsöldner" is essentially a synonym for "armoured pikemen": "the Doppel-sölder, that is the armoured pike".

Second, while large greatswords were used on the battlefield, only a small fraction of the infantry carried them. They were rare weapons. It was unusual for as many as 5% of the infantry to carry them. Imperial regulations of 1570 described the ideal Landsknecht batallion (Fähnlein) of 400 men as composed of 100 armoured pikemen (50 of them Doppelsöldner), 50 unarmoured pikemen, 50 soldiers with either halberd or greatsword (usually the majority carried halberds), and 200 "shot" (soldiers with guns). Other versions of the ideal Fähnlein were: 500 men, with 200 shot, 200 pikemen, 45 halberdiers, 45 soldiers with boar-spears, and 10 Schlachtschwerter; and 300 men, with 186 shot (42 with heavy muskets), 82 Doppelsöldner with pikes (and armour), 18 halberdiers, and 14 Doppelsöldner with Schlachtschwert (and armour).