The OP is quite old, but I will attempt to give an answer (for centrifugals) so that hopefully the thread can be resolved.
The guideline of 30 m/s max (often 35 m/s is acceptable too) velocity at compressor suction is because the vendor shall guarantee performance. Generally, but not always, the guarantee point is located in the best efficiency area which itself corresponds quite well to the area where the predictability of performance is "good" (which boils down to a statistical concept). This has to do with the smoothness/regularity of the flow as it flows across the inlet plenum towards the first stage, which is also the condition on which the machine is tested. Keeping in mind that a too low velocity (<10~15 m/s) is also not desirable for that purpose. This reasoning can be also made on discharge side (losses across discharge scroll).
In other words, if you have an alternative case operating on the choking limit line, or in the vicinity, it is clear that the velocity of the gas at the suction flange for that case will be well above 35 m/s (50 m/s is not unusual) ; yet, it is not forbidden to run on such operating condition but as far as predictability is concerned, the vendor wont guarantee such point performance, at least on a standard approach. If it is required to guarantee performance for such extreme cases (deal breaker), a risk assessment will be conducted, which typically implies extra contingencies and/or increased and hidden tolerance (determined by the probability to fail performance test vs. built in tolerance).