on our server there is running v3.0 rc3 and i can tell you its possible on every de_map to place the serpent wards on every bombspot till the bomb is planted - that means even while planting the bomb...if the bomb is planted you cannot place the wartds next to the bomb - thats right, but all the time before the c4-timer starts! and the wards stay there till the person who set them up dies...
to say it with other words: yes its not possible to place a serpent ward on a beeping bomb but you can plant a bomb on a serpent ward
so it would be great to disable the wards on the bombspots at all...
dont know exectly what about placing them next to hostages but for example on cs_italy its possible to block all entrances of the house with the wards

and i can tell you, its very difficult to get in and out of the house to rescue the hostages, even if there are only 2 shadowhunters in T-team....
if necessary i can record a demo which shows you how to do that stuff with the wards...
greez