Actually there are no Irish vital records (births, deaths, marriages) before 1845/1864.
It depends on the religion and the particular church where your ancestors attended. Church records such as baptisms would record all children baptised not just the wealthier of the congregation. Not many churches (of any religion) in Ireland have records pre-1800 (many before mid-1850s do not exist) so the real problem is lack of surviving church records rather than economic status of individual families.
Now back on topic.... DNA Testing - Why Not