How much do your dental hygienists do for periodontal practice?

Lots and lots. Most dental practices that have a periodontal component rely very heavily on the dental hygienists. Routine maintenance and monitoring of periodontal health should be coordinated between your dental hygienist and dentist.
Quite alot. In our periodontal practice, our hygienists spend a good deal of time with you and know your mouth the best. They are active in discussing the conditions they see and the consequences of those conditions, they help identify oral hygiene needs, work with you on your home care, and communicate with the periodontist about what they see.
Invaluable. I could not/would not practice without hygienists. I could not see/care for all my patients without their support. They examine, clean, teach and motivate our patients. I still examine everyone, but they might see something in their 1 hour that i might miss in my 5-10 minutes.