Let me correct my simple statement as it was too simple. The DER EE DE-5000 puts out different voltages depending on the size of the capacitor and the frequency used. You cannot be sure you are not turning on semiconductors without checking each time. It also will not measure capacitance and ESR of big capacitors in 10kHZ or 100 kHz mode so you are restricted to 100, 120 and maybe 1kHz, depending on the size as I have not tested above 2200uFd in my hasty tests.
So yes, you can test the ESR of small capacitors at 100kHz and have less than 0.5V, most of the time. Are small caps likely to be the ones you need to worry about ESR? Not usually I think as they tend to not be aluminium electrolytics, which are usually the type that need to have their ESR value checked. If you need to check big aluminium electrolytics in circuit, then you will need to use 100Hz, 120Hz or maybe can use 1kHz with the DER EE DE-5000 and then you have the potential of higher voltages being applied than are OK for in circuit testing.
And yes, I was wrong, most specs I could find on ESR or "impedance" of electrolytics were specified at 100kHz. This actually makes the DE-5000 unsuitable because it will not measure bigger electrolytics at 100kHz.
My apologies for not being clear and not checking the facts. My error about specs does not change the suitability of the DER EE DE-5000 for in circuit testing for ESR.