The Local Defence Forces (LDF)- to be distinguished from the National Defence Forces (NDF)- have constituted the network of Iranian and Hezbollah-backed formations of Syrian fighters during the war. In 2017, regulations emerged that could be interpreted as allowing for service in LDF units to be equivalent to compulsory and reserve military service in the regular Syrian Arab Army, and it would appear that some LDF fighters have indeed been considered to have completed compulsory and reserve service within the LDF (see, for example, the biographies I compiled of two Syrian fighters from Homs province who were killed in U.S. airstrikes in March).
The problem however is that these sorts of regulations can be seen as creating an inherently unfair system in which it becomes more advantageous for a Syrian wanted for military service to evade the regular draft and then join up with one of the Iranian and Hezbollah-backed units, which generally feature better salaries and working conditions for fighters than the regular army. It would thus appear that in more recent times (the past year or so), there has been a trend of transferring some LDF fighters over to the regular army. For the Iranians and Hezbollah, this transfer confers the advantage of reducing financial burdens of supporting these fighters.