Not necessarily. There are some similarities, in that both question types ask you to read between the lines, but there are some crucial differences.
An assumption is a necessary link between a piece or pieces of evidence and a conclusion. Therefore, you are looking for the answer choice that you think the author must believe for the author to stand by her argument.
If the author says, "I am going to buy food tonight. Therefore, my family will enjoy dinner." One assumption is that the author is going to bring the food to the family. Another assumption is that the family will be willing to consume this food. Yet another assumption is that the family will take pleasure in eating the food once it is brought to them.
If the author does not believe all of these assumptions, and other assumptions you can come up with, then the argument does not hold.
Inference questions, however, ask us to interpret subtexts. There is no subtext in the argument above about family strife or a previous pattern of food hatred. But in a reading comp passage, there very well may be.
Generally speaking, assumptions are "missing," whereas inferences take information that is "hidden."
Additionally, Reading Comp passages use flawed logic far less often than do critical reasoning passages. If an author is arguing for or against something in a Reading Comp passage, chances are there is not much missing from that passage.
