I just brewed a turbid mashed lambic with the same yeast. Yeast took a few days to reach CA from the east coast (it was hot outside), went into the fridge for two weeks before brew day, and pitched with no starter. The wort received pure O2 for one minute and then airlock was attached. Like you I did not see any activity for three days after pitching, then a light krausen formed for a week. I will not be racking into secondary as I hope the brett will feed off of the autolysed yeast over the next two years, and IMO without purging everything with CO2 I believe you will introduce more O2 by racking than opening the airlock in primary. In your case the only way to verify that the sacc strain in the blend was viable is to take a gravity reading and use sensory after you check the sample. If it has not dropped I would pitch another strain of sacc asap.