I have not worked with Guillermo but I would try not to worry too much. I've heard nothing but wonderful things about Dreams and their wedding staff - and I'm positive they won't let your special day be a disaster. I'm working with Magda for our November wedding and although it does take her some time to reply (especially as of late with the staff changes) she does respond and answer all of the questions I have. If you are unsettled and don't feel completely confident I might suggest reaching out to Tammy who runs this forum. She can't step in to help as she doesn't work for Dreams but she may have a contact of someone in the department or be able to suggest an external wedding coordinator. Another thought - Do you have a photographer or any other external vendors you're working with for the wedding? Having someone in Cabo that may know Guillermo or have an "in" at Dreams might help too. Perhaps they could stop by next time they're around or call on your behalf??
Either way, your day will be FABULOUS and you and your fiance will love every minute of it. Keep us posted and let us know how it goes. Good luck!