How to Verify SNAT is working ?

i understand you have to check connection table or tcpdump.

e.g.

[root@ve10:Active] config  b virtual bar80 list
virtual bar80 {
   snatpool mysnatpool
   pool foo
   destination 172.28.19.252:80
   ip protocol 6
}
[root@ve10:Active] config  b pool foo list
pool foo {
   members 200.200.200.101:80 {}
}
[root@ve10:Active] config  b snatpool mysnatpool list
snatpool mysnatpool {
   members {
      200.200.200.201
      200.200.200.202
   }
}

 connection table

[root@ve10:Active] config  b conn server 172.28.19.252 show all
VIRTUAL 172.28.19.252:80 <-> NODE 200.200.200.101:80   TYPE any   1/0
    CLIENTSIDE 192.168.206.33:59234 <-> 172.28.19.252:80
        (pkts,bits) in = (7, 1216)   out = (7, 4962)
    SERVERSIDE 200.200.200.201:59234 <-> 200.200.200.101:80
        (pkts,bits) in = (6, 4922)   out = (6, 1176)
    PROTOCOL 6   UNIT 1   IDLE 2 (300)   LASTHOP external 00:01:e8:d5:d4:47

 tcpdump

[root@ve10:Active] config  tcpdump -nni 0.0 port 80
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on 0.0, link-type EN10MB (Ethernet), capture size 108 bytes
16:22:20.666129 IP 192.168.206.33.59236 > 172.28.19.252.80: S 198530642:198530642(0) win 8192 
16:22:20.666175 IP 172.28.19.252.80 > 192.168.206.33.59236: S 3936556914:3936556914(0) ack 198530643 win 3780 
16:22:20.668126 IP 192.168.206.33.59236 > 172.28.19.252.80: . ack 1 win 16695
16:22:20.668167 IP 200.200.200.201.59236 > 200.200.200.101.80: S 634129559:634129559(0) win 4380 
16:22:20.669160 IP 192.168.206.33.59236 > 172.28.19.252.80: P 1:625(624) ack 1 win 16695
16:22:20.669170 IP 200.200.200.101.80 > 200.200.200.201.59236: S 1644104907:1644104907(0) ack 634129560 win 5840 
16:22:20.669178 IP 200.200.200.201.59236 > 200.200.200.101.80: . ack 1 win 4380

another option would be to look on one of the nodes, you should any traffic from the F5 originating from the SNAT address. Microsoft have TCPView which is excellent for a visual netstat.