Yes, the ride will get less damped in hot weather (feels "softer") but you don't say wether you prefer this.
In cold wether the oil will cause the shock to damp more and the ride will feel firmer. Bear in mind that shock absorbers turn all that energy they absorb into heat, so they run warm most of the time anyway.
If your budget will allow it, the koni ones are adjustable and tend to last forever (they are rebuildable), so with a turn of the adjuster you can have the ride of a Caddy or a Corvette.
'73 Jensen Interceptor (Resting)
Giant Full Sus Mountain Bike