When inputting image rgb values to MLP, should I divide by 255?
The component values are often stored as integer numbers in the range 0 to 255, the range that a single 8-bit byte can offer,

Yes, If you divide by 255  the range can be described with a 0.0-1.0 where 0.0 means 0 (0x00) and 1.0 means 255 (0xFF). 
Normalization will help you to remove distortions caused by lights and shadows in an image.

Refer to this Normalize RGB