His daughter's request, for such it might be considered, of being admitted into her family again before she set off for the north, received at first an absolute negative. But Jane and Elizabeth, who agreed in wishing, for the sake of their sister's feelings and consequence, that she should be noticed on her marriage by her parents, urged him so earnestly, yet so rationally and so mildly, to receive her and her husband at Longbourn, as soon as they were married, that he was prevailed on to think as they thought, and act as they wished. (Chapter 50)

I do not think Mr. Bennet allowing them to visit means he has forgiven Wickham or Lydia. He has only taken Lizzy’s and Jane’s rational advice to “notice” Lydia on her marriage because by doing so he puts a sort of parental approval on it and helps to strengthen the respectability of the marriage. As Lizzy and Jane argue that is what is best for Lydia, her feelings and consequence. I think it was the right thing for him to do after all the entire to-do about finding her was not only to recover her but also the honor and respectability of the family. It would be sort of silly for Mr. Bennet to fail in following through on this last bit to sanctify the marriage. Also comparing Wickham to Mr. Collins is not a compliment. ;D