In March, a Hyatt representative confirmed on FlyerTalk that free 'membership sites' would be included when applying for a BRG.
However, they have stated that the terms and conditions have changed and that no membership sites, whether paid or free, are included in the BRG requests now.
The terms are clear on Hyatt's website that you need to find, 'a publicly available and immediately bookable room-only rate on the Internet' so where a membership site only showed the rates upon log-in, they weren't meant to be honored. To now exclude those sites that do show publicly available and immediately bookable rooms seems like a big backwards step for Hyatt to make.
FlyerTalk have a wiki thread showing recent success and failures of member applying for a Hyatt BRG.
Galahotels.com (with persuasion)
Onhotels.com (successful on phone but trouble with online claim)
Skoosh.com 07/11/14 (original denial but successful with persuasion)
Getaroom.com (recent success also)
Hoteltravel.com (membership site)
Otel.com (membership site)
Galahotels.com (membership site – but also recent success)
You could always try your luck, seeing as some sites can work with agent persuasion, but overall it looks like Hyatt are really tightening up…