I guess over here 'ground' is third form of grind and if you grind something out you produce that same thing in poor or boring way. All it's impact is ground out might mean all it's impact is reproduced in boring way. For questions like this you better write it in context. Thanks.

To me, this means that almost all of the impact has been negated. Ground out, as Azmat says, is the past tense of the word grind. As I understand the statement, it means that something occured to cause an impact, but subsequently, the impact had been gradually reduced to almost nothing by another factor (it was ground away to nothing or 'ground out')

Ground out is terminology used in baseball, which means a play in which a batter is put out by hitting a ground ball to a fielder who throws it to first base before the batter touches that base. (被杀出局) Almost all of its impact is ground out basically means it has no consequent impact.