It is known that GTA series have three separate universes, the 2D universe, the 3D universe and the HD universe, in the 3D universe, se have GTA San Andreas, a game of PS2 platform, one of the most famous GTA games and the first in the franchise that presented three cities instead of one, in the HD universe, se have GTA V, the game takes place in the same state of GTA SA, this time with a bigger map and impressive graphics, but the two games are from distinct universes, so any of the events of GTA SA happened in GTA V, nevertheless, i've gathered a few evidences that show that GTA SA and GTA V takes place in the same universe!
First evidence: Cris Formage and the Epsilon programThe Epsilon program are highlighted in GTA V, but its existence come from GTA SA, including its founder Cris Formage, that can be heard in a radio show in WCTR, this could possibly means that both games are in the same universe!
Second evidence: the possible presence of Grove Street Families in GTA VThe street gangs Ballas and Vagos are your main enemies in GTA SA, and appears in GTA V with a less importante in the story, but Grove Street Families seems to be out of the game, but there's a gang very familiar to Grove Street called the Families, they wears green clothes and are deadly enemies of the Ballas, just like Grove was in GTA SA, so its possible that the Families are actually Grove Street Families, but the Ballas has taken Grove Street somehow, without Grove as a territory, there was no reason to keep this in the name, so they became known only as the Families.
Third evidence: the CJ's outdoor in GTA IVIn GTA IV there's an advertisement outdoor showing CJ in a fancy suit, showing that Carl may have became rich, probably because of his friendship with the rapper Madd Dogg and the Triad leader Wu Zi Mu.
Fourth evidence: the HD remaster of GTA SAIn commemoration for the 10th anniversary of GTA San Andreas, Rockstar released an HD remaster for Xbox 360/PS3, this fact could possibly brings GTA SA from the 3D universe to the HD universe!
Unfortunaly, there's many things that can bring down this theory, the first one is that Cris Formage is in fact in GTA SA, but this not necessarily means that both games are in the same universe, maybe Rockstar just taken the idea from GTA SA, and put it in GTA V, without any connection in the story of both games.
The second is that maybe the Families are just a reference to Grove Street Families, without any connection to GTA SA.
The third is that the CJ's outdoor in GTA IV may be just an easter egg, and not enough evidence to prove that GTA SA is in the same universe.
The fourth is that even GTA SA having a HD remaster, it not necessarily mean that the game is on the HD universe.
Nevertheless, it is just a theory, do your believe it, or not?