Actually not. 1.f4 d5 is indeed a reversed Dutch but I have always been slightly skeptical about 1.f4 because of 1...Nf6! which avoids the weakening of the e5-square and at least temporarily stops e4. Correspondingly I find 1...d5 a slightly illogical reply which to some extent justifies White's first move. That's why I consider 1.a3!? d5 2.f4!? an interesting sequence of moves while 1.f4 d5 2.a3 appears rather meaningless.
But is there actually any advantage in having the extra a-pawn move in a reversed Dutch? There obviously are certain Dutch lines with an early ...Na6 that simply become impossible to play with a pawn already occupying that square. However, I assume that with a deep understanding of Dutch strategy and a little imagination it should be possible to steer for positions where a3 is useful. Here is an example where White succeeded wonderfully:
N.McDonald - B.Thipsay, Banwell mem London 2001
1.a3 d5 2.f4 Nf6
Quite possibly Black should immediately ensure control of the long diagonal with 2...g6.
3.Nf3 g6 (Dia)
Black has chosen a sensible set-up that can be completed without taking on too many obligations in the centre.
4...Bg7 5.Bg2 0–0 6.0–0 c5
Finally Black accepts his role as White! Probably 6...c6 would have given comfortable equality.
7.d3 Nc6 8.Nc3!
Probably this is White's best chance to make something out of his pawn on a3. From a comparison with the parallel position with reversed colours it seems that 8.Qe1 and 8.c3 are sensible alternatives.
8...d4 9.Na4! (Dia)
After 1.d4 f5 2.Nf3 Nf6 3.g3 g6 4.Bg2 Bg7 5.0–0 0–0 6.c4 d6 7.Nc3 Nc6 8.d5, 8...Ne5 is a little more popular than 8...Na5 but odds are much better that White can make use of a3 in this line.
9...Qd6 10.c4 Ng4
In the reversed position the main continuation is 10.b3 a6. However, 10...b6 could nevertheless have been considered as White's score in the reversed line is 59%. Only experience can tell how much difference one tempo can make but in a sharp position where both players pursue different plans, it may well make the difference between a win and a loss.
Philosophically White can claim some success as the two main continuations in the parallel reversed position are 11...Rb8 and 11...a6. What's more: in the 28 games with these two moves, the score is 9 wins for White, 7 draws and 12 wins for Black!
11...e5 seems a more consistent follow-up of Black's 10th move.
12...b6 13.bxc5 bxc5 14.Rb5 Rxb5 15.cxb5 Nd8 16.Qc2 Ne6 17.f5 gxf5 18.Nh4 Bf6
Fritz suggests 18...Nc7 with roughly equal chances.
The pawn structure is quite murky but White's advantage is not in doubt as his piece activity is superior.
19...Qe5 20.b6 axb6 21.Nxb6 Ng7 22.Nc4 Qc7 23.Bf4 Qd8 24.Nh6+ Nxh6 25.Bxh6 e5 26.a4 Re8 27.a5 Ne6?
27...Ba6 would have been a better try.
This wins an exchange thanks to the hanging bishop on f6.
28...Bg7 29.Bxe8 Bxh6 30.Bxf7+ Kg7 31.Bxe6 Bxe6 32.a6 Qa8 33.Qb1 Qxa6 34.Qb8 Bxc4 35.Qf8+ Kg6 36.Qf5+ Kg7 37.Qxe5+ Kg8 38.Qe8+ Kg7 39.Qf8+ Kg6 40.Qf5+ Kg7 41.dxc4 1–0