I'm using GCC4TI, which is a C compiler. I've read the included documentation along with some tutorials (there was a nice one on technoplaza.net, back when it was still up) and every single time sprites were declared as arrays of either unsigned chars, unsigned short ints or unsigned long ints. Example smiley face sprite:
unsigned char sprite[] = {
0b01111110,
0b10000001,
0b10100101,
0b10000001,
0b10100101,
0b10011001,
0b10000001,
0b01111110
};
Equivalent to:
unsigned char sprite[] = {0x7E, 0x81, 0xA5, 0x81, 0xA5, 0x99, 0x81, 0x7E};
As far as the standard assembler for 68k programming, to my knowledge it's always been A68K, which originates from the Amiga (in fact, some of the early Fargo programmers seem to have used only this system) so microsoft BMP's kinda seem out-of-place.