His townland at marriage strengthens the probability that he was, therefore, the same Robert that was working as a servant in 1901 for John Gillespie.
I had thought this family, in nearby Killyless, may also be worth checking further, as the head of the household is widowed:
http://www.census.nationalarchives.ie/pages/1901/Antrim/Ballyconnelly/Killyless/924641/whilst it is transcribed as Grigg, the original has no dot above the 'i' and is more than likely 'Gregg'. However, the 1911, as Gregg, suggests she only had 5 children, and all five are accounted for in the 1901. Checking Griffiths Revision books suggests her husband may have been a Daniel.
There is another Gregg household in the townland, but the head is an Alexander. Another neighbouring townland, Loan, also has Gregg households, but the heads there are Williams.
If your Robert was from the Ballymena area, based on his age and approx birth year of 1883/4, there is only one potential Robert senior death between then and 1908. It being a Robert who died in 1898 aged 48. However, the lack of any obvious birth index entry for your Robert in the area could make it difficult to link the two. Still, if you haven't already, always worth checking the 1898 death.