[morzh]

You can use any cap you want.
The scope impedance is at least 10M which means that whatever capacitance you use it will not load the oscillator.
You may have problems seeing a signal at units of MHz / 100s of kHz through 5pF (300kOhm at 100kHz).

Also the working frequency of an oscillator is dictated by it's resonant tank and not by its load (until you really overload it of course).

Use 10nF / 600V or so, you'll be fine.