Unless it's really difficult to gather and treat (such as a hill flock), it's advised to not combine any other treatments with the Hep-P, especially in pregnant ewes. Mind, you have to balance the physiological stress of all the meds against the psychological stress of two gathers and treatments - which is a judgement each of us has to make in our own situation.
I agree with this wholeheartedly.
Gathering sheep stresses them no matter how friendly/tame they are (and pushes them into close proximity with each other) and every gather should be on a risk vs reward basis. Obviously gathering to vaccinate or to worm (IF they have worms) is a no brainer, but unless there is a problem, I am of the opinion that sheep should be left alone.
I was speaking to somebody who manages grazing projects some years ago and he said that it was always the overenthusiastic beginners that seemed to have most disease problems etc, and it was the same people who were constantly gathering sheep.