Agents have nothing to do with italics. Italics/underlining is for the editor and typesetter, and it has nothing to do with typewriters. Underlining is a proofreaders' mark, and all editors use proofreaders' mark. So do typesetters.
Writers really need to get over thinking that anything is done as a holdover from typewriters. Pretty much nothing is. Underlining is used because a great many manuscripts are still edited by hand, and when you edit by hand, you must use proofreaders' marks to keep everyone on the same page.
There is an editing process, and things change during this editing. If, as an editor, I find something that isn't italicized, but needs to be, the only way I can show this is by underlining it. If the writer uses actual italics, there are no two things the next editor and the typesetter must watch for, and that's a pain in the ass.
It doesn't much matter which you use with an electronic manuscript that will be edited on a screen, though some publishers still want underlining because they use electronic proofreaders' mark that also maintain underlining for italics, but for print manuscripts that will be edited by hand, you're taking a big chance if you use actual italics. Odds are good that the published novel will have some mistakes in it.