Answer

Yes. In Śvetāmbara Jain tradition, Jamāli is regarded as Lord Mahāvīra’s son-in-law. ( jainpedia.org)

Explanation

Some Jain sources also describe Jamāli as Mahāvīra’s nephew and son-in-law. At the same time, a few historical studies note that the exact canonical details are not completely clear. ( wisdomlib.org)

Spiritual Understanding

Jamāli is remembered in Jain history mainly because of his later disagreement with Lord Mahāvīra and the early schism associated with him. ( jainworld.jainworld.com)

Takeaway

So, the simple answer is: Yes, Jamāli is traditionally considered Mahāvīra’s son-in-law. ( jainpedia.org)