No way,no how, is Sol going to get a chance to hit Vito in the hospital. Between the "private detectives" and the Corleone guys,any unusual activity is going to be noticed and dealt with immediately. Any ripple in the normal routine,any new face on the staff,the newspaper coming five minutes late,any thing out of place would shut the place up tight as a vault.

Having said that,Sollozzo may have been successful using unconventional means.Let's say that he had a contact who could have poisoned Vito's food while it was being made,or an employee who would go on the take to spike Vito's IV bottle.

If he didn't get killed in the hospital,I agree that Vito would not have been an easy target once he got home,and Sol would not have had another crack at him.