I extracted these two sentences from an English newspaper. I want to know why hyphen is used before 'who served' and 'hoping'? Who actually served the cabinet? were it the ministers?

Those making phone calls to ministers - who served in the previous cabinet- have been pleasantly surprised off late at the speed at which their calls have been answered.

Others had done so - hoping to be appointed back to the cabinet.

By the way, what does off late mean?

They are not hyphens, but rather are en-rules used to indicate a clause in parenthesis.
"off late" - a misprint for "of late",
Students: Are you brave enough to let our tutors analyse your pronunciation?

Those look to be hyphens but as an expert, I have to trust you. By the way, what are en-rules? Before asking, I did try to do some research but had hard time trying to find anything that I can understand online. Help. I think you can use a hyphen in most cases where a comma is used and also, it can replace a clause in parentheses under the right circumstances. Thank you.
"en-rules" = printer's term for what most people call dashes.
Yes, you could use commas or parentheses "( )". People tend to use dashes to indicate a longer pause before and after the clause if the sentence is spoken.