Perfectly acceptable to operate the B737-800/900 with only one operating reverser, which would of course mean you have asymmetrical reverse thrust. There are no x-wind limits per se.
From my company's MEL:-
OPERATIONS (O)
NOTE: Thrust reverser deactivation can result in the illumination of the MASTER CAUTION and ENG annunciation when performing a Master Caution recall.
1. During rejected takeoff and landing rollout, use the operative thrust reverser normally and, use the rudder and brakes to maintain aircraft directional control.
2. For wet and contaminated runways, apply weight and V1 reduction by no reverse thrust option in the QRH.
3. For dry runways, no performance correction is necessary.