I believe the implication is that a chocolate syrup might not have sufficient conductivity to provide a reliable magmeter measurement, with the suggestion of Coriolis as an alternative measurement technology.
I would suggest measuring a sample of the liquid for its conductivity at whatever temperature the mag will see the liquid to determine if the liquid's conductivity meets the mag's minimum spec.
For the good of the forum I will volunteer!
Send me a barrel of chocolate syrup and I will test it in a mag flow for you! And then my kids will test it in a milk shake, on their cereal, with their lunch ...
Otherwise - use the internet - http://www.eolss.net/sample-chapters/c10/E5-10-01-02.pdf
Lists the conductivity of milk chocolate as easily compatible with magnetic flowmeter ranges.
Chocolate syrup is basically an aqueous solution - so I would expect it to be conductive. Modern magnetic flow meters are very sensitive (1μS/cm and upwards is good depending on size) - I reckon you will be fine. I am not aware of a viscosity limitation (maybe I will learn something?).
I say give it a go!
You will of course need to be conscious that this is a hygienic food product - and instruments must be selected accordingly.