uuencoding will have a slightly lower single-character entropy than the ASCII armor PGP uses because just about every line begins with the letter 'M'. This will skew the distribution slightly. But a better way of distinguishing uuencoding and ascii armor is to see that in falls in the same entropy class, and then just looking at the alphabetic subsets used.
It's not that simple. The entropy of a byte is the number of bits needed to represent it. If what is uuencoded is extremely repetitive, the entropy will be low, maybe even less than one. On the other hand, if it were random data, it would just be slightly lower than ascii armor. Binaries are somewhat repetitive, so they have somewhat less entropy than random data. English has a lot of redundancy, so it has a low entropy. e