No, 1.7~3.0V is the recommended operating range, out of which you will shorten device's lifespan.
Absolute maximum is the range where you will permanently damage the device.
So, operating the OV5647 at 3.3V is not good design .
Most cameras have an AVDD of 2.8V, some 3.3V and few 2.5V.
For DVDD (core), it is either 1.2V, 1.5V or 1.8 V.
And for DOVDD (I/O), it is either 1.8V, 2.8V or wide range from 1.7V to 3.0V at least (only a few extend to 3.3V or even 3.6V).
Thus, you should absolutely provide a way to choose PE, as it is done in the AllWinner reference design! If you use 3.3V for DOVDD, you will damage them very quickly!
As for the attenuation you observe on the scope, it is probably due to the scope's ADC antialiasing low-pass-filter, but it is not real. What is your scope analog bandwidth in MHz?
See attached charts: