Is it permissible to accept financial aid (marriage assistance) offered by a company owner, knowing that it was not in exchange for a service or expediting a transaction, but rather out of appreciation for friendship?

If the assistance is from a friend, out of friendship and not for your job, then there is no harm in accepting it. However, if the assistance is from a governmental company where you work, and assuming it is from the company's funds, then for it to be permissible, the manager must be authorized to disburse it.