Does Zakat have any role to play in the fiscal system of Muslim countries or should it be free from government interference?
This is purely my view. Maybe you can also with Islamic scholars.
Zakat shouldn't have any role in the conventional fiscal system. In the conventional fiscal system, taxes are collected and they are use for government fiscal requirement, such as for operational expenditures as well as development expenditures. Whereas, zakat is obligatory for all affordable Muslims as stated in the Qur'an. And zakat collection should be distributed to the specific recipients (asnaf) as stated in the Qur'an. There are eight recipients who can receive zakat, ...
Zakat is similar to tax in the conventional economic system. However, their concepts are different. Through zakat, incomes are distributed directly from the rich to the poor. Whereas, taxes money are mostly distributed indirectly through government spending. The identified zakat recipients will receive the zakat money directly, whereas, in the tax system the benefits are indirectly received by them.