Thats a very good question you asked i have a big udor pump attached to a gearbox an it has supports on it.I think they all should because that massive pump it just attached with bolts if not supported i have seen the bolts wear and break over time lots of time i might add.
I asked the same question when I went to a gear drive and 8 GPM,..the pump weighing 40 lbs itself. I was also told not to worry about the weight issue on the gear box,... by very credible sources and I listened to them and haven't had an issue. I still look sometimes though,Ha,Ha,..
I was also told by one of the members here about snapping bolts,..he told me to use Grade 8 bolts. I did,..and I will replace them every season,.probably overkill but it's very cheap insurance.
I guess its the same school of thought on double feeding any pump 8 gallons and up.Just like having good insurance an reliability on the jobsite.Might not ever need it but its there double fed and supports on my 12gpm udor with gearbox.I have seen others break but it might have been the cheaper gearboxes or in relationship to the grade of bolts that you mentioned who knows.