If you are using scene2res to convert your GTA:SA map (original, TC, etc) into a MTA server format, then you must make sure to have the permission of all content creators before offering the game files on a public server. In our case this is most likely Rockstar Games/Take2 themselves. I cannot help you with content ID (very very complicated) so you have to act responsibly/in good faith.
If you are creating scene2res converted maps for personal use (you are the only one playing on the server) then you have nothing to worry about. Generally I cannot recommend the use of scene2res on any servers anymore because it is too easy for the common user to get it wrong. Instead a new tool is required that would directly convert the game files from a rightful game installation itself. Every connecting MTA player would have to perform that conversion himself. This new and different process would be considered fair-use.