The risk of salt intrusion in the FRG of the hull (usually into 'just' the matting layer) is that the deposited 'salts' will continue to draw water into the laminate ... and if the laminate or resin was poor to begin with will increase the risk of the future development of 'osmotic blisters'.

Your careful examination of the hull for the presence of 'blisters' should be your guide, as if there are many many blisters and especially 'large' blisters then there 'may' be a problem. If the hull was 'quality' constructed with a full wet-out with resin then there shouldnt be a problem, especially if the boat has been barrier coated. That stated, I'd be quite wary for the presence of DIY 'blister repairs', especially with a boat that has move from salt to fresh water. For me, DIY 'blister repairs' are usually a prime deal breaker.

A fairly good reference source on 'blisters' (but certainly not to be taken as 'gospel'): http://www.yachtsurvey.com/blisters.htm