I don’t know for definite if the dress is ivory, but grey certainly wouldn’t clash with either white or ivory. Personally I think it would be a really classic and elegant look if you had your bridesmaids in grey, but you can avoid it looking too pale by combining this with pink/purple bouquets. Deeper shades would provide a good contrast, and you can always use pastels for the centrepieces. It’s ok to use different shades of a particular colour, as it can add an extra dimension to the design.

Hope that helps!