I once had an DEC AlphaStation die on me and I took the dimms (they looked funky) out of it and stuck it into a p2 I had laying around. Sure enough, it worked! Don't give up hope, even if it is listed as proprietary memory, it may still work.. On the other hand, the memory for my current servers is way more than 168 pins, they're huge.
In all my days using DEC products, I've never seen any silly products such as "simm doublers" from them. People who buy server class hardware rarely employ cost cutting measures such as doubling anything. Chances are this is a perfectly useful dimm (likely with parity).