Вы просто хотите UNION ALL
?
SELECT NEWID() as Id, ss.Id as SkillId, ss.Name, sc.Vote,
sc.CandidateId, sc.Id As ScoreId
FROM dbo.SoftSkills ss LEFT JOIN
dbo.Scorecards sc
ON ss.Id = sc.SkillId
UNION ALL
SELECT NEWID() as Id, ss.Id as SkillId, ss.Name, NULL, NULL, NULL
FROM dbo.SoftSkills ss;