Personally, I think denial on their part would be pointless at best and downright insulting at worst; but, It would depend on how the drug was processed.
If there's enough Crystal Release remaining in the final product then other shinobi would probably connect the drug to the only Crystal Release Clan in the world.
How much crystal release can be detected in the final product is entirely dependent on how the drug is produced. We can talk about the details if you really want to theory-crunch it. I'm well-versed in this topic because Hyōryugetsu Hōzuki from the other Naruto RP utilizes drug-enhanced genjutsu which is produced through her kekkei genkai. Her version of ninja-meth is a plant-based narcotic; she ingests the plant and then extracts the narcotic bits to produce the drug. You could achieve something similar by using crystal release to
process the drug instead of to
create it from scratch.
I agree with thatguy on the distribution though. You'll have to do a bunch of thinking about
how you want to distribute this drug. Criminal Cartels and Minor Shinobi forces
do exist and they could act as intermediaries if needs be.
The ideal situation for your clan is probably to have a distributor within the other nations, some other Clan that you smuggle the drug to in bulk and then allow them to distribute it within their own borders.
How effective your distribution is will determine your profit margin. That and a bunch of other factors; production cost, production quantity, etc. will determine how realistic it could be for the Clan to use this as a main means of income.
For example, the largest Clans
maybe have a thousand members, while most clans can reasonably be expected to have a few hundred.
If we say the Kyoyakishi have...800 or so members, an upper-end Clan, then how many of these people could be working on drug production? 100...200...300?
How many tons of crystal-drug could 300 shinobi produce?
Guren is a Jonin, so she can produce quite a hefty amount of crystal; but, whether the Clan wants to invest its Jonin into drugs instead of their ninjutsu or medical divisions is up to you.
Details aside. You won't need highly specific answers to these questions (e.g. you won't need to know exactly how much crystal drug could be produced), just an idea of what the logistics are is enough for me.
Once you've got that down then yea, I could see it becoming a viable source of income.