The term appears 311 times in the Vimuttimagga.
This is an early 6th c translation, and later zuochan became the term for “sitting in Chan/Zen.”
As for being unequivocal about the Indic original of that term in this text, that is difficult.
First, the translator, 僧伽婆羅, whose name is variously transcribed as *Saṃghabhara or *Saṃghavara or *Saṃghavarman, and is translated into Chinese as Zhongkai 衆鎧 ( ‘Armor of the Saṃgha’ ), also translated Mahāyāna materials, such as The Prajñāpāramitā as Taught by Mañjuśrī, (T.233) which is a translation of the Śaptaśatikā prajñāpāramitā ( ‘Perfection of Wisdom in 700 Lines’); the Jñānālokālaṃkāra-sūtra (T. 358); Mahāyāna Ratnamegha sutra (T. 659), and so on, so one may question whether the original of the “Vimuttimagga” was in Pali rather than Sanskrit or some related Indic language. Some East Asian scholarship has taken to rendering its Indian title as Vimuktimārga.
Second, different translators used different equivalents for Indic terms. Zuochan ren *could* represent yogi, yogāvacara, yogācāra, yogācārya, etc., or something else. In the broadest sense, zuochan ren should be understood as “a serious practitioner.”
Hope that helps.
Dan