So long as the plug is the correct dimension and has a adequate heat range then it will be fine, most problems occur because of extremes of temps ie a tuned engine going slow all the time will foul, but sticking in a hotter running plug to combat carbon fouling and it may damamge at higher speeds/loads, so at best it is a comprosmise.
I can't comment of skyline plugs as don't know the heat range etc, but there is a lot of hype about anything if it makes a profit!!
tabetha