Yes.  The engine is designed to work best within a certain temp range. If
the engine is too cool then all the variously carefully clearenced engine
parts won't expand properly causing excessive wear-and more.  Any good oil
cooler (I would think) should have a pressure relief valve or something to
prevent the oil from flowing through it when the temp is too cool.
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I met a guy who had done this.  He lived on the east side of the sierras,
near Yosemite, wher it freezes all winter ands bakes all summer.  The oil
cooler was mounted on top of the bus (?!) and i dont remember if it was a
hand switch or automatic to route the oil to the cooler or not.    It was a
painted up 62 or 63 23-window.

nice guy too, I saw his shop (hey looks - old vws!)  called Marginal
Mechanical . coming back to california from Grateful Dead tour one summer in
Gus, the 59 bus, and he gave me a couple oil pan nuts, which had fallen off
somewhere.   I remembered the oil cooler, but not that it was a 23 window.  

When i was back in the area, and suddenly needed old bus parts,  I visited
him again, and he  helped out, providing a replacement for the bent trailing
arm.  :)  "there's an old front suspension out back, you can take off it what
you need"

clara