If UDLD (normal -not aggressive-)is only configured on one switch A and not on the remote one (switch B),
will switch B counter/add UDLD packets received as runt (smaller than 64 octets packets) or as any other error ?
Will the switch B react regarding its hardware or software ? (a cat3750 switch will not react as a cat2950 switch as switch B) ?
UDLD (or any other protocol!) will never create packets shorter than the minimum legal length for the media. (64 bytes for Ethernet). Also, UDLD won't do much if it's only on one end - but the multicasts it generates will simply be ignored by the other end.
The situation would work like this:-
Switch B successfully receives traffic from Switch A on the interface. However, Switch A does not receive traffic from Switch B on the same interface. UDLD detects the problem and disables the interface.
Ideally you could have it on both sides.