It's worked in other countries, the Netherlands being a case in point in recent times. There was a farmers party in Ireland in the 20s and Clann na Talmhan in the 40's and 50's.
If if focuses solely on farmers, it will get votes but possibly not enough to get TD's elected. If they can broaden the base to make it a genuine rural Ireland party, then it might get a handful elected but that is all it needs to hold the balance of power
However, different farming groups have different aims, the ICMSA would have a very different outlook from a small farmer in Mayo for example. Likewise, the green/organic grouping will have different views. But if they can get a collective agenda, and focus on other areas and not just farming, so rural housing, planning, roads etc, it could do ok