Most Orthodox people in Slovakia are natives. Vast majority are Rusyns, then some Ukrainians (mostly descendants of early 20th century's Ukrainian migrants), few Slovaks are Rusyn. Pravoslavni in Slovakia make just under 1% I think. Concentrated mainly in eastern Slovakia.
There are only few Orthodox Christians in Moravia and Czechia, mostly natives in case of Moravians and mostly migrants or their descendants in case of Czechs.

Thanks for the detailed answer.