It makes more sense to compare RAID 3 and RAID 4, since the two only differ in the stripe size (they both use a dedicated parity drive). Note that RAID 2 does essentially the same thing, except on a bit level, but at least Wikipedia claims that RAID 2 is not used in practice (albeit not entirely surprisingly that claim is tagged "citation needed"; it's usually much easier to provide references for positive than negative claims, so this ought to be taken with a grain of salt).
RAID 0, in contrast, employs no parity at all but is striping only.
In RAID 4, each drive holds a multi-byte block (presumably the block -- stripe -- size is configurable on the controller because there are tradeoffs between block size and performance).
In RAID 3, the block size is effectively fixed at 1 byte.
Blocks are simply groups of a (largely arbitrary) number of bytes. Everything on storage can always be thought of as bits and bytes (particularly if we define a byte as a contiguous set of 8 bits, with alignment if you want to get fancy), so yes, by that definition, bytes are what makes up blocks.