So plumbing up my crap and I have a single 1" drain from a 30g fuge going to the sump. I just wonder if I'll be able to dial in enough flow for the fuge to operate.
How are you feeding the "fuge?" Put simply, with a single drain, you are limited to an open channel drain (for safety reasons) aka durso. 1" pipe may flow 50 gph before it starts acting up, perhaps a tiny bit more. Since the concept that a "fuge" (excluding seahorse as occupant) requires low flow is completely false, that does not seem like a really good plan.
You would get better performance out of a 1.5" drain, open channel, at around 350 gph before the problems start.
"Operate" is a rather ambiguous term, and I think the term you are looking for is "effective." Considering how most folks run them and what they put in them (more of what is in the tank,) they are effective for creating more production, (nitrate factories) and not much export. Couple that with low flow rates, and they are even more effective as nutrient sinks.
No reason to not put the full flow of the system through, but all in all, the system will not do better with it, and it won't do worse without it.
There are reasons to run a fuge, keeping seahorses, culturing more exotic macro algae species (gracilaria, caulerpa, halimeda, etc) that you don't want nibbled on...