Yes, and many/most motorcycles don't have straightforward access to anything that would allow the RPM to be directly measured by some other means, either. This situation has been discussed elsewhere. It's fairly likely that only the idle test will be enforceable. Any method of measuring the RPM by some other way is open to being questioned.
Example: my ZX10R.
The stock (digital) tachometer is not accurate, in fact we KNOW that it has designed-in error in it. (It reads high, which actually acts in your favour, but this is not legally important, the point is that it is not accurate - full stop.)
Accessing a spark plug lead on that bike for using an inductive tach (A) is a 4 hour job because ALL the bodywork has to come off, (B) by the time this is done, the engine will have cooled off, and SAE J2825 requires that the test be done with the engine at normal operating temperature, (C) this bike uses coil-on-plug ignition with no exposed high-tension leads, I'm not sure that an inductive tach will even work.
There is no access to the end of the crankshaft that can be accessed with the engine running without spraying oil everywhere.
It is likely possible to access the actual engine RPM via Kawasaki's proprietary scan tool (the bike is not OBD-II compliant, so a normal scan tool won't work) but this is something that not even the dealers have, nevermind the cops, and that tool only works on Kawasaki, they'll need another special one for each manufacturer and possibly different generations of them as the various fuel-injection systems evolved ... For bikes that have OBD-II ports, a regular OBD-II scan tool ought to work, but that covers only a fraction of the bikes that are out there.
