Rosegreen seems to be a pretty modern invention. An older version of the name is Roesgreen. When considered in the light of other local placenames like Lowesgreen, Price's Lot and Waller's Lot it would seem that Roe was the beneficiary of a Cromwellian land settlement. I think Bawn79's first instinct was correct and the site was used for sun worship. Interesting that the graveyard which is still in use occupies the site still and that an old church was built on it.
ROESGREEN or LOWESGREEN
a hamlet, in the parish of St. Patrick's Rock, barony of Middlethird, county of Tipperary, and province of Munster, 3 miles S. from Cashel, on the road to Clonmel; containing 62 inhabitants. Fairs are held on Aug 2nd, and Oct. 23rd; and one of the R.C. chapels of the union or district of Cashel is situated here.
I thought the name may have had some roots in the Pallasgreen/ grian or sun goddess. However from the Gaelic for Rosegreen, it seems that it literally means rose green.
This mound is just off the R686, there is a church across the road that looks like it may be built on a low mound. Perhaps they are both barrows. The field this mound is in is up for sale for a housing development so this may be the last we ever see of it.