Running rams with suckling ewes ,in most breeds not a problem however some like dorset horn /ile de france can take the ram even when suckling , even on commercial farms rams are often run with suckling ewes. Your question was specifically asking about running them with ewe lambs only , and while yes they should not be cycling the rams may stimulate them , and this forum continually has lambs born at all times of year . An old farmer near by seems to have lambs at all times of the year as the rams are never removed and the ram lambs never cut