Yes. Croatia is supported by the EU roaming calls/text add-ons.
http://www.48months.ie/membership-plans/going-abroad
But bear in mind that there is no cost advantage in buying an EU roaming text add-on versus paying for texts from your cash credit balance.
In fact it will be more cost effective NOT to buy an add-on if you don't send 100 SMS messages (remember that long text messages may use more than one SMS).
And there may be no or little cost advantage in buying an EU roaming calls add-on versus paying for outgoing and incoming calls from your cash credit balance depending on how you use these services.
Personally I don't bother with EU roaming add-ons any more and just top up my cash credit balance when travelling.
Also the roaming charges should be changing again soon:
http://europa.eu/youreurope/citizens/consumers/telecoms-internet/mobile-roaming-costs/index_en.htm
Hope this helps.
