都 vs 也 in "连。。。都／也" structure
连...都... and 连...也... are interchangeable as a structure. In fact, in the structure 连...都..., 都, as an adverb, means 也! 

In your case, the sentence could be rephrased as 


  他什么都吃，连狗肉 也 吃。 我们连一次 都 没见过。


However, in the first sentence, 他什么都吃, 都 can not be replaced by 也. Here, 都 means 'all'.