Back in 2015, when there was a slump in tourist arrivals, the Vietnamese Ministry of Culture proposed that Australia, but not Ireland be given visa free status. Since then, nothing has been heard of this proposal.
See: https://www.vietnam-visa.com/uk-france-australia-likely-enjoy-vietnam-visa-exemption/
BTW Australia sent 66,000 troops to the Vietnam War and Thailand also sent troops. Thais now get visa free entry, as they are a member of ASEAN. Australia was supposed to get visa free status, as it is regarded as a friend of ASEAN, but this proposal has died at tourist numbers have risen.
Ireland does not figure in the calculations of the Vietnamese Government.