Would Nuclear Weapons be as destructive in ship to ship space combat, as they are on the ground in an atmosphere?
As far as I know, the big damage from Nuclear Weapons planetside is the massive blastwave that can pretty much scour the earth, with radiation and thermal damage bringing up the rear.
But in space there is no atmosphere to create a huge concussive and scouring blast wave, which means a nuclear weapon would have to rely on its all-directional thermal and radiation to do damage.. but is that enough to actually be usful as a weapon in space, considering ships in space would be designed to handle radiation and extreme thermals due to the lack of any insulative atmosphere?
I know a lot of this might be supposition based on imaginary future tech and assumptions made about materials science and starship creation, but surely at least some rough guess could be made with regards to a thernonuclear detonation without the focusing effects of an atmosphere?
Others have answered you question about non-directed nuclear blasts in space already. They don't work the same way as in atmosphere; lack the blast or the thermal heat, etc.
Enter the Casaba-Howitzer, a theoretical nuclear shaped charge that shoots a directed plasma stream at near light speed. This idea came about in the 60s along with nuclear blast propulsion.
The name comes from the casaba melon, a variety of honeydew, because the lab was "on a melon kick that year," naming various projects after melons and having already used up all the good ones.