It seems like you created the rule using "fwaccel dos rate add". If you used "fw samp" to create the rule, then the problem may be that you need to perform a "flush true".
For reference, here's what I see when I create a similar rule (using fwaccel dos rate add) and then do watch -n .1 'fwaccel dos rate counters "<5ff335d1,00000000,335016ac,0000723b>"':
==================================================
Rule UID: <5ff335d1,00000000,335016ac,0000723b>
Policy: 2
FW Index: -1
SecureXL Index: 1
Timeout: unlimited
Max Concurrent Connections: unlimited
New Connection Rate: unlimited
Packet Rate: 0
Byte Rate: unlimited
Max Concurrent Connections Ratio: unlimited
New Connection Rate Ratio: unlimited
Packet Rate Ratio: unlimited
Byte Rate Ratio: unlimited
Action: drop
Log Type: regular
Concurrent Connections: 0
Connection Rate: 0
Packets: 5
Bytes: 490
Violated Limits: packets-per-second
==================================================
The "violated limits" line item should indicate that the rule is being violated, but only while packets are being sent from the blocked host.