It is.  I own
some three or four cards which have four 30-pin SIMM
 sockets and are designed to plug into a 72-pin socket. 
 As I look at these, I notice that they're all adapters as opposed to
 something that gangs up multiple SIMMs to create a higher capacity
 "SIMM".  Anyone seen anything like that? 
 
Yes, I have a few of those around somewhere...  The SIMMs have to have
the "right" geometry and/or the system has to be able to handle the
resulting geometry.  I seem to recall that they have locations on them
for surface mount chips and switches (to allow the geometry to be adjusted)
but they are unpopulated on the ones I have.