Working with support we determined that the issue is that the varbind was a string type, where the lookup value needs to be an integer. Since I can't change the varbind type an event procedure to modify the value to an integer did the trick.
My test trap has the string CFM.Service030911.1249.Network-1-2.down.1249 in the varbind. The following event procedure returns the value 30911 as an integer and successfully does the table lookup using { T TableName 10}.
0xfff01113 E 20 P "CreateEventWithVariables( \
{ C CURRENT_MODEL }, \
{ H 0xfff01114 }, \
SetEventVariable( \
GetEventVariableList(), \
{ I 10 }, \
ToUInteger( \
GetRegexp( \
ToString( \
{v 10} \
), \
{S\"^CFM.Service([0-9]*)\..*\"}, \
{U 1} \
) \
) \
) \
)"