Yes this is correct as it is exactly correspond to the dynamic range definition. But in order to be accurate on low signals, your signal power should be 15 dB more than the noise level (e.g -95 dBm) to not suffer from over-gain losses.
Also, while looking at high power signals, be aware of the span you are measuring on,meaning - a peak signal of 0 dBm can be mistaken if the overall span band power (power measured on the entire input span) is more than 0dBm, than the input signal can be saturated