To be able to reliably use the remote outside, it must be RF. IR requires line of sight so even if it has a strong emitter (or two) like the Home Theater Master remotes, it won't work reliably unless you can point it at the IR sensor of the equipment.
I can use my HTM MX-350 in IR mode from the patio too - but it's only because when standing at the grill with the patio door open I can aim it right at the IR sensor on the receiver.