Oh Lordy. I feel for you. It appears as though there is no one at your job that knows what they are doing.
Dobutamine is an inotrope. It's used typically for squeeze and to increase cardiac output, which could in turn, increase renal perfusion/urine output. I would not say that I have generally seen it used in cases of CHF where the patient's primary need is to be diuresed, however. Typically if someone's CHF is so advanced to need dobutamine (or other inotrope) management, they have a SG catheter placed to guide therapy. Many, many patients that come into the hospital for CHF just get IV diuresis these days and sent home with their cardiac meds (oral) optimized (newer therapies for long term low EFs/CHF include biventricular pacers as well, etc.) I'm not sure that using dobutamine in this way is an old concept or not -- but I am thinking that it is. If a patient has a chronic, low EF, I'm not sure that a day or two of a dobutamine gtt is going to improve their long term prognosis, but I'd have to do a lit review to say this definitively.
Are you thinking of dopamine? That is more commonly used, low dose, for renal perfusion/increase UO (also controversial and old therapy, and in my experience, only works about 5% of the time.)
Either one of those drugs (dopamine or dobutamine) are not considered diuretics, to answer your first question. I'm not sure why your ICU nurse friends don't know about dobutamine. It might not be used often in their practice, but it's an old-standby ICU drug. They should have at least been taught about it in their ICU classes/orientation period.
Using the admission ("dry") weight is the standard of care everywhere I've ever worked for weight-based drips. Where is your nurse manager on that issue? That should be reinforced to the staff.