Yes, Pasture appears to be implemented properly. For example, from a sample game:
Shepherd Simple(Plr 1) has 41 points and took 27 turns
32 cards : [6 Copper, 1 Silver, 10 Estate (10▼), 7 Duchy (21▼), 1 Pasture (10▼), 7 Shepherd]
Big Money Ultimate(Plr 2) has 59 points and took 28 turns
38 cards : [6 Copper, 10 Silver, 8 Gold, 4 Estate (4▼), 1 Duchy (3▼), 8 Province (48▼), 1 Pasture (4▼)]
Yes, there are simple Shepherd strategies that can beat BMU. Just not the one outlined in the OP. I quickly built one by buying Gold and Silver like I was playing Smithy-big money but using Shepherd instead for draw. Tweaking to buy Duchies/Estates earlier helped a little. But the results are nothing to write home about (loses to Smithy-big money quite handily). But I did not try too hard. There is space for OP to explore.