It seems to depend on the Garda. In relation to Kilmahuddrick, the garda I spoke to said that there was a very young population there and 'high levels of anti-social behaviour with youths.' Said he didn't want to say any more than that because he could be held liable.
A garda in Tallaght garda station was much more forthcoming about an area I enquired about. Told me under no circumstances to buy there, because 'i'd wake up every morning wondering if my car was still outside'.
When I contacted Lucan Garda station enquiring about a certain estate, the Garda said she couldn't give me any sort of advice because 'it wouldn't be fair to the estate agent trying to sell the house.'
I thought that was utterly ridiculous as surely the Gardai should have the best interests of the public at heart rather than the estate agents! Maybe she had relations in the business!
So from my experiences, it can vary dramatically how forthcoming/helpful the gardai can be in these situations. In my opinion, they should always be honest and helpful to anyone who makes these sorts of enquiries.
I doubt it could be construed as slander because it was a comment said in a private conversation rather than a public forum. Not sure if there's an garda offical policy on giving this type of advice.