Would lipo under the buttocks make it look bigger?

Yes it can.  However, it needs to be done in select patients with the right anatomy and somewhat conservatively.

I would not recommend Liposuction under the buttocks because that area supports the buttocks and you most likely would be unhappy with how the buttocks would look after. Best of Luck. 

In order to accentuate the buttocks, I use a unique buttocks contouring technique by performing liposculpture of the surrounding areas, specifically the waist, hips, and thighs. This approach allows me to
reshape the buttocks and highlight your natural curves without necessarily
making the butt larger itself. The end result will allow your butt to become more defined and appear larger.

I explain to my patients who need liposuction of the "saddlebag" area that contouring of this region makes the butt more shapely with better contour.  It will not necessarily make your butt see more prominent, but it makes the thighs look slimmer and longer separating them from the backside.  Most patients who undergo the procedure are delighted with the transformation.  Meet with a ABPS board-certified plastic surgeon to discuss your options. Best wishes,Jon A Perlman M.D., FACSDiplomate, American Board of Plastic SurgeryMember, American Society for Aesthetic Plastic Surgery (ASAPS)ABC-TV Extreme Makeover SurgeonBeverly Hills, California