Yes, normally linkerspiegel as one word means a mirror that is always on the left. Right now I can't think of any other standard combination of a left and a right mirror. You can also come across linkerbuitenspiegel. The rear view mirror is achteruitkijkspiegel (just as odd as in English since all mirrors give you a view to the rear but only this one has it in its name).
If you see linker spiegel (so separate words), it will be a mirror that currently happens to be on the left. Other examples: the right tree (de rechter boom), the left book (het linker boek), the left person (de linker persoon).
Some other examples of standard left and right combinations: body parts (right leg=rechterbeen), clothing (right sleeve=rechtermouw), sports field positions (left midfielder=linkermiddenvelder), infrastructure (right lane=rechterrijstrook), river banks (left bank=linkeroever, the standard way is looking downstream, e.g. Antwerpen Linkeroever is the part west of the river Scheldt (Schelde)).
This means a difference can be made between de linkerschoen (the left shoe, one for your left foot) and de linker schoen (the left shoe, currently on the left).
Mind you there is no rule for this, what I described above is a guideline, see this explanation in Dutch.