Yes you are as with all other Welsh "r"s, (Though remember "Rh" is a letter in and of itself and has a different pronounciation.) Though if you can't roll your "r"s then don't worry, I've spoken Welsh since childhood and I have to make a concious effort to roll my "r"s. To hear it with a trilled "r" go to "Forvo.com" and type in "Hydref" in the search bar.
Thanks, both EllisVaughan and Ibisc. I knew that 'rh' was always and unvoiced trilled R but just wasn't sure about the single R being lightly trilled at all times. I will always give the Rs at least a quick tap of the roof now :) I could trill my R easy since childhood when I used to use it for a pretend machine gun. What a phonetically diverse language welsh is, to have two different types of trilled R, along with two different types of dental fricatives and the welsh LL sound.