r and ʀ represent two different Elder Futhark runes, generally called *raido and *algiz respectively. The latter is used for a sound derived from Proto-Germanic *z, so many people (including me) prefer to write it as z; it's easier to type and harder to misread. But the weight of tradition is strong and many scholars continue to call it ʀ, so if you're interested in Norse, you should get used to seeing both.
Hróald is the normalized classical form of the name; runic inscriptions are not very consistent in spelling, and the distinction between hr and r was not always observed. This may have to do with the distinction being lost in some dialects (we know this distinction completely disappeared later on, which is why the modern form of the name is "Roald") or just come from the orthography not being standardized (hr was probably a graphical convention for a voiceless
/r̥/, which didn't have its own rune, and r is also a plausible way to represent that sound).