I have done it on another forum. 
once.
It was completely opportunistic, I was on the talk boards, and someone had The. Most. Amazing life situation, and I was coincidentally advertising for a research subject in the area without much luck (I kept getting folk call, but it was a sensitive subject and they would usually bottle). I sent a pm and explained everything, included my full rl contact details, apologised hugely for contacting them in such way, and explained my interest. We have met up several times now, and it really was a one-off, I just read the situation and my head exploded. 
I knew I had to talk to that one person specifically. it was the most perfect combination. Truly serendipitous. We discussed participation via email, then telephone, and then arranged for the first interview at the sponsoring university. After that, once we had established an rl status, we met in various places that were convenient to the participant.
I'm sure that you were a great nursery nurse and have valid input to whatever they are whatever for, but mn prefer researchers to post a call for participants on the media/ non members area, even if they are members... Personal approaches are not generally de rigour and are a bit spammy.
I got away with it by flattery - there really only was one person in that situation, and it was mutually appreciated by both parties that the alliance was beneficial to all concerned. I'm not so sure that your circumstance would have made it so appealing to break with protocol...
It's probably the only time I'll ever do it. And I would have backed off instantly if the response had been 'no ta.' I would have been gutted. But it was one single participant for an in depth analysis, not some crappy survey thang that's all about the numbers, or someone looking for an easy way to get quotes for an essay. I very much doubt that any research that has passed an ethics committe had 'send personal messages to complete strangers' in their proposal.
I'm a total hypocrite, really.