Is is possible to use non-hydraulic fluids in a hydraulic system in an emergency?
Is it possible? Sure. Theoretically. Once.

I can't speak to your Aeroflot scenario without more details, but broadly speaking any liquid will work as "hydraulic fluid" within certain limits: At the most basic level all that is required is that it be incompressible and flow at an acceptable rate (i.e. It is a liquid with a viscosity that falls within a certain range).  Engine oil is frequently used as a hydraulic fluid for certain applications (constant-speed propellers on small aircraft), and special-purpose hydraulic oil for others (the brakes on small aircraft).



There are some challenges to using any old liquid as "hydraulic fluid" though, which are why I say this is only theoretically possible (and probably only once). The two big concerns are the fluid's operating temperature range - its freezing and boiling points - and its corrosion potential.   

Let's consider MIL-PRF-5606H (a typical hydraulic oil) and ordinary lemonade as examples:  

Operating Temperature Range

In terms of temperature 5606 hydraulic oil has a much wider operating range than lemonade: It's "pour point" is below -60°C and its boiling point over 175°C, while lemonade's operating temperature range is probably close to water: It will freeze somewhere close to 0°C and boil somewhere close to 100°C (the exact numbers will depend on the chemical composition of the lemonade).
If we use both of these fluids in a brake system there is a chance the lemonade will boil when the brakes are applied (creating a gas pocket that's compressible, and reducing brake effectiveness), or that it will freeze in flight and the brakes will fail to apply because the ice is blocking the lines. 

Corrosion Potential

As far as corrosion potential 5606 hydraulic oil is a mineral oil with some red dye in it: Since it doesn't contain dissolved water or electrolytes it's generally non-corrosive. Lemonade on the other hand is nothing but water and dissolved electrolytes (mainly citric acid to make it taste like lemon) plus sugar and a few other things. If we ran hydraulic actuators on this stuff we should expect them to corrode (rust) and eventually fail.

So it's possible that under the right circumstances an airplane could complete a flight with lemonade, water, etc. as "hydraulic fluid", but having done so the maintenance department will have to purge the "creative" fluid from the system, and probably follow some steps to remove any corrosive residue from the system (possibly up to and including replacing major system components). Long term operation in such a condition would probably damage components to the point where many of the system's moving parts (actuators, valves, etc.) would need to be replaced.