Yes IDSM can be inline device.
Regarding throughput, it's best to do a test.
I beleive a single IDSM can do 500Mbit/s (Marketing numbers, actual performance will depend on features enabled etc etc) via ECLB you can take up to 4 devices to provide up to 2Gbit/s throughput (if traffic is load balanced properly).
If you want to check current load, you can check either stats in IDSM itself or if you want traffic statistics:
show intrusion modu {NUM} data-port {1|2} traffic
example result:
Intrusion-detection module 7 data-port 1
Specified interface is up line protocol is up (connected)
Hardware is C6k 1000Mb 802.3, address is 0012.4374.290c (bia 0012.4374.290c)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s
input flow-control is off, output flow-control is unsupported
Last input never, output 00:00:44, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
2 packets input, 164 bytes, 0 no buffer
Received 1 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
188437 packets output, 89695206 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
