事実は and 事実には are both the topicalization of 事実に. 事実には is more common, though. The point is 事実が(反駁/反論の)余地がない is wrong. 事実 is always the target of 余地がない and can't be the subject of it. As for 用がある, this phrase can take a person both as the subject and the target, therefore に can't be omitted. (In other words, は always indicates the subject in ~は用がある. When topicalizing the target, ~には must be used.)