Is a group of pigs called a skulk?

No, a group of pigs is called a 'drift' or a 'drove'.

Other names for groups of pigs:

More than one pig can be called swine because the Word swine can be both the singular or plural form of that alternate Word for pig or pigs as in: "How many swine do you have in your herd?"

There are other collective nouns used for groups of these types of animals like the above example of a "herd of swine". Such as:

The collective name for a group of,

• Swine - can be either 'drift', 'doylt', or 'trip' - e.g., "A drift of swine",
• Boars (male pigs) - is also 'herd' - e.g., "A herd of boars",
• Wild boars - is a 'sounder' - e.g., "A sounder of wild boars",
• Pigs - is 'drove' or also 'drift' - e.g., "A drove of pigs",
• Hogs - is 'parcel' - e.g., "A parcel of hogs".