Is Snow load added to the Gravity load case in AutoPIPE?
Yes and No.
Please see the following AutoPIPE help section:
Help > Contents> Search Tab> enter "Snow Analysis Overview" (include the quotes), press List Topics button, double click on the selected topic (Snow Analysis Overview) from the list provided to see more information.
Note, the Limitation at the bottom of the help page.
"Gravity" - AutoPIPE Load Case