Modern defense Benoni setup with Ne7 I saw a DVD with GM Roman Dzindzichashvili, where he recommended, when white avoids the Dzindzi-Indian by playing 3. e4, that black adopt a Benoni setup but with the important difference of playing going Ne7 instead of Nf6.

[FEN "rnbqk1nr/pp3pbp/3p2p1/2pp4/2P1P3/5N1P/PP3PP1/RNBQKB1R w KQkq - 0 7"]
1. d4 g6 2. c4 Bg7 3. e4 c5 4. d5 d6
5. Nf3 e6 6. h3 exd5


White I find this this attractive when indeed black manages to take control of the central dark squares and then play Ne7-f5-d4, I find that white with exact play can make black's position quite uncomfortable. This is especially so when white does the following:
1. When white recaptures cxd5 instead of exd5 (in the exd5 case the white king is more exposed, giving black dynamic possibilities) when the f5 square is not as definitely under white's control, certainly so when the light squared bishop goes do d3. Roman recommends black playing for an f5 break in these positions, but seems to me to be super-risky.
2. Prevent Bg4 and thus Bxf3 by playing h3
3. Going for a quick Bf4 before black gets to play Nd7, pressurizing d6 and intending e4-e5.

My questions is: Is it possible to state in general terms that when plays cxd5 and h3 and a quick Bf4 --> play Nf6, otherwise play Ne7? Someone who has another take on this question?
Like all positions in chess, it's incredibly difficult to come up with general terms and common rules for openings. The particulars of each situation must be judged separately.

That being said, the idea that Dzindzichashvili is recommending is a good one - Ne7 stays flexible (and keeps your bishop open) and allows you to quickly strike at white's center with f5 (a crucial pawn break against d5-e5 structures). As you said, this pawn break can be double edged because you are creating a critical hole in your position: e6. So only consider it if there is no chance for white to sink a knight or bishop onto e6.

Now to respond to the line you are suggesting: I would argue that this plan still works in this line as well. Moreover, striking in the center while you are castled and your opponent is not seems principled as well.

[FEN ""]
1. d4 g6 2. c4 Bg7 3. e4 c5 4. d5 d6 5. Nf3 e6 6. h3 exd5 7. cxd5 Ne7 8. Nc3 (8. Bf4?? Bxb2) O-O 9. Bf4 f5!? 10. e5 dxe5 11. Bxe5 Nd7


I agree that you're still in a cramped position, and you obviously have to be careful about the d pawn pushing forward. But let's look at the dynamic positives here as well. The center has blown up and white still needs 2 moves to castle. You have a queenside majority that can instantly start pushing with a6-b5. And you have the ultimate blockader on d7 already setup. So there's no worries there. There are also interesting opportunities for f4 followed by Nf5. These are the types of explosive lines you are signing up for when you allow your center to gain a huge center as early as move 3.

Side note: If you truly want to trade off your light squared bishop, then your best bet is to play 5. Bg4 instead of e6.