no, oclhashcat supports the full 0x00-0xff range. but i'm not sure you can get oclHashcat to read a null character from an hcchar file since getline(3) is null-terminated. (edit: actually no, it does indeed read a null character from a hcchar file just fine.)
normally if you want to use null in a custom charset, you need to use --hex-charset. you can also use $HEX[00] in a wordlist, or use --hex-wordlist.
normally if you want to use null in a custom charset, you need to use --hex-charset. you can also use $HEX[00] in a wordlist, or use --hex-wordlist.