I feel you on the frustration. When I had my nerve blocks they told me to pump and dump for five days. FIVE.
I tried, but my frozen milk was bad -- not so much bad as just soapy tasting. I forget the specific reason why, there's even posts here about it on the pumping board. The short of it is I have to scald my milk before long term storage, and I hadn't and he refused it. And we tried formula. And he refused. I literally sat there with a little plunger and force fed him my milk because he wouldn't eat and it had been nearly a day. After trying that once or twice I broke down and gave him my milk anyway. Not eating was worse (in my eyes) than getting some of the meds given to me.
It wasn't until I had to get them again and I found out what the meds were and looked them up on Hale's site that I realized I could have gotten away with dumping for a day (and I had had a day's worth of milk in the fridge) and then giving him my milk again.
So, the second time I didn't have the sedation and I dumped for a day and then fed him as per normal.
Unfortunately I think they take the option of being overly cautious -- saves them on the lawsuits. I can't completely blame them, but it is very frustrating when you go in letting them know you breastfeed and want things that are compatible and they don't know. Because then you are stuck trying to find the info yourself and pray your sources are good.