Hitler attended his first Nazi rally originally as a spy for the military, sent to report on them. When he eventually turned and fully joined the party, did the government ever try to undermine and sow distrust of him by 'leaking' the fact he used to be their agent?
And either way when it eventually did come out, how did it effect him?
It was no secret. Hitler himself admits in Mein Kampf that:
"One day I received orders from my headquarters to find out what was behind an apparently political organization which was planning to hold a meeting within the next few days under the name of 'German Workers' Party' - with Gottfried Feder as one of the speakers. I was told to go and take a look at the organization and then make a report."
The context here is that the Reichswahr, profoundly unhappy with the new Weimar Republic, was dabbling in all sorts of murky far-right political groups. Karl Mayr (head of the Bavarian 'Information Department') had at his disposal around fifty informants/instructors whom he used to monitor Munich's political milieu and provide training to soldiers on the correct (ie nationalist and anti-communist) political line. Connections like this, eg Ernst Rohm, proved invaluable in providing the early Nazi party with funding and connections to the wider nationalist movement.
So as far as I know there was no impact from Hitler's admission to informing. Quite the opposite: it showed that he had taken the 'correct' (ie right-wing) line during the chaotic revolutionary period. (Conversely, Hitler's autobiography does not mention that he spent time as an elected representative to soldiers' council during the Bavarian Soviet Republic.)
Source: Kershaw's Hitler