For solaris 10 and 11.1 at least.
I believe iostat -xn gives you r/s and w/s which combined is the IOPS of the nfs resource:
user@server:~$ iostat -xn 2 2
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
58.1 0.0 7196.9 0.0 0.0 0.1 0.4 2.2 0 5 somenfsserver:/share
0.0 57.4 0.0 7340.6 6.7 0.6 116.0 10.8 4 10 anothernfsserver:/share1
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
747.3 0.0 95660.1 0.0 0.1 3.1 0.1 4.2 4 86 somenfsserver:/share
0.0 748.3 0.0 95787.5 158.5 10.0 211.8 13.3 100 100 sanothernfsserver:/share1
r/s + w/s = IOPS, in this case I am reading from share and writing to share1.