Double taxation relief with Ireland and USC

Salary payments from Ireland have both Irish PAYE and USC deducted and I am wondering if both the PAYE and the USC contributions are counted as tax paid for the puposes of double tax relief whem completing a UK self assessment form?  My instinct was no but have come across some info online which suggests that both are deductable for people living in NI working cross border in Ireland (not the case here) which has thrown me a bit.

On a 2nd point is is normal for an employer to be deducting Irish PAYE, Irish USC and UK NI from a salary paid from Ireland to a UK resident?

TIA