Are oo and or yoo the same vowel sound?

Most grammar sources say yes. Although the concept of long vowels are that they "say their name," the long U can be represented by a long OO as in rule, dune, and Flute -- these Words follow the pattern of long vowels in Words ending in silent E.

The sound "YOO" actually contains a consonant Y (y-glide) and follows several consonants, as in cute, mute, mule, fuel, feud, and view, as well as in Words that start with U such as uniform, unicorn, and unique.

The reason that some classify them as different sounds is that using the term "long U" can be confusing where there are both long OO and long YOO variations that are both Words, such as mute and moot, cute and coot, feud and food, and fuel and fool.