The only thing I can say is, IMHO, the 'pressure' the weights create is different than the 'pressure' that is experienced in chi sau, so I don't believe you are really gaining anything. General fitness and that kind of weight training is the best in that regard. In relation to technique, the lop-sau, poon-sau and other chi sau related drills (or, to say just chi sau) should prove more than enough to develop technique specific endurance.
Also, IMO, the forms are not nessisarily meant for strength development, rather they are more for learning basic positions, coordination, and technical development. Having weights could ingrain a bad habit of being tense when you want to be *relaxed* or *soft*.
Sapere aude, Justin.
The map is not the Terrain.
"Wheather you believe you can, or you believe you can't...You're right." - Henry Ford