Flynn has already proved that his funding from these leaders has come with strings attached. He has already spoken publicly in favour of Recep Erdogan and claimed that the United States needs to view the country as an ally and a key priority. This is despite the fact that Erdogan's administration has been committing grave human rights abuses and stands accused of funding ISIS. Putting this man in a position of real political power could prove problematic as he may serve his own financial interests above the interests of the country.
It's pretty hard to be objective about folks who give you lots of money. Also, it's pretty discouraging to have a national security chief who seems to be in Russia's pockets. It's absolutely a conflict of interest, and will make me question whether he's thinking about the country or his own financial benefit if he's forced to take action adverse to Russia's interests.
Yes, it is a conflict of interest for Trump's national security chief to have taken money from Putin and Erdogan. How can a national security chief make wise decisions involving Russia when he has benefited from the leaders of those countries. Would he be able to make a decision that harms these two individuals?
Individuals from other countries should not be giving money to high ranking U.S. officials. This only causes the people who receive the money to vote for policies that favor these countries. The national security chief should give the money back. This would avoid making it look like Trump's staff is trying to profit from the election.