Safe to connect SDR to home Cable?
35 dBmV means "35 decibels stronger than 1 mV", or about 10^(35/20) = 56 mV RMS. 56 mV is a pretty small signal, so it's unlikely to damage any input that wouldn't be completely destroyed by the ESD of casual handling.

There is still the possibility (though unlikely) that the input signal may be too strong for the receiver and would cause clipping. This may make it hard to separate a weak signal of interest from harmonics of a stronger signal. If that happens, you could try placing an attenuator between the RTL2832u's input and the cable.