Is what the suitor did—dissolving the engagement—permissible in Sharia in this case, and is he allowed to reclaim the money and ring he gave to the fiancée, knowing that they were part of the dowry and not a gift?

If a woman works for a company that transports alcoholic beverages, and this work entails khalwa (private seclusion) with a non-mahram man, in addition to working in an interest-based (riba) bank and wearing tight clothes in front of non-mahram men, then these are all forbidden and reprehensible matters. If you clarified the impermissibility of these matters to her and she did not desist from them, then you were right to break off the engagement. You are permitted to reclaim what you paid her if it was part of the mahr (dowry) and the marriage contract had not yet been concluded.