Can you vacuum seal Ziploc bags?

You could, in theory, vacuum seal some Ziploc bags but it would not be a preferred method because the motive for vacuum sealing in the first place is preservation/shelf-life extension through air extraction.

A Ziploc bag is designed to be opened and easily accessed at intervals. You would lose the benefits of vacuum sealing.

Vacuum sealing is designed to extract air and protect goods from moisture damage and other contaminants. For this hermitic heat seal packaging is the best solution to work with both the vacuum sealer machines and give the products optimal protection.