I'm not aware of any Webster County census being on-line.
And, as I said, with just the initials being provided, I can't be sure that E. Rathbun and B. Davis is the couple you seek or that E. Rathbun is the Eugene Rathbun who lived in Christian County. I only know that there is no other Rathbun, first initial E. on Christian County personal property tax records between 1894 and 1898.
It did occur to me after I said that Vern had to be Maggie's son or Eugene's son prior to their marriage that there was one other possibility - that he was adopted. There are so many discrepencies in the ages, children born to Maggie and still living, length of marriage etc. that it's hard to be sure what the truth is. I do know that sometimes adoption has been secret and not even told to the child. As for Icey Belle Davis, if she did marry a James Rathbun, I don't find them. However, that is entirely possible. There are many places to live, and I can't have looked at all of them. If she did actually marry Eugene, it appears likely that she had died before 1898. The question of the boy's parentage, however, remains unanswered. Sorry. I don't know the answer, just these possible leads.