Not yet. In the NBA I think you have to win at least 3 championships in a row to be a dynasty or 5 within a ten year period with a core group of players. The Celtics of the 60s (9 titles), the Lakers of the 80s (5 titles) , The Bulls of the 90s (6 titles), and to a lessor extent the Lakers (5 titles) with Kobe/Fisher from 2000- 2010.
If Miami wins this year and next year they will be counted among the elite teams. However if they only win two titles (including last year), they will be looked at like the Detroit Pistons of the 80s who won titles back to back. No one considers that team to be a dynasty.