I've only seen Irish bands playing on St Patrick's day. The band in Delaney's in Wan Chai were awesome, but I don't think they're local, I think they fly in from Cork or Dublin every year (though not 100% on that, worth checking at the bar). Another pub I saw live Irish folk was in Murphy's on Nathan Road in TST, again on St Patrick's so not sure if it's a regular thing,..they were defo local though, as the fiddler lives on Lamma and busks at the bottom of the mid levels escalator most days,..could ask him.
And,..Dublin Jack's has indeed closed down,..RIP my beautiful, beautiful mecca of booze, your are sorely missed and I wish I knew you and your bountiful delicious beverages sooner...