Probably...
If they are different speed ratings (DDR speed), they will be fine, but run
at the lowest common speed.
If they have different latency timings (CAS) then you might encounter
problems. The CAS speed is usually 2, 2.5 or 3.
Of all potential variables, brand does not matter.
If motherboard doesn't automatically set them to
appropriate, error-free timings then manually set that in
the bios to the slowest common denominator for both.
Test the config for several hours with http://www.memtest86.com prior to booting the operating
system to avoid potential file corruption.