Well, it probably wouldn't be viable without military customers (nor would any private/semi-private large rocket programme). And Arianespace is ultimately a joint venture between Airbus and Safran, both of which are, amongst other things, defence contractors; in that regard it's little different to, say, Boeing.
Ariane 5 IIRC was the first that wasn't built from ICBMs - previous was built from ICBM projects retargeted for space launch, and ofc all the rocketry tech base in the manufacturing companies is still from ICBM manufacture.
Ariane 4 at least would also have used main rockets designed explicitly for civilian purposes; no-one was building liquid-fueled ICBMs by that point (and, past the _very_ early days, no-one really wanted ICBMs that _big_). The solid boosters would certainly have a military heritage, though.
Ariane was designed from scratch (mostly), it's just that everyone involved first cut their teeth on military use.
The previous Europa rocket had parts from ICBM.
As for liquid-fueled ICBMs - Soviet Union invested much longer into liquid-fueled ICBMs, including very heavy ones, something that paid off in keeping their space sector in expertise.
I'm differentiating mostly on who paid for the development in particular company, and would that development exist without military. Apple doesn't fall under that (even though they survived 1990s heavily thanks to federal sales, iirc) - they build the company on top of consumer market.
Compare this with SpaceX where DoD funding was crucial or most of other US launch vehicles that trace directly to early ICBMs. Ariane was built by companies from defense sector continuing development started from ICBM work - but Arianespace was purposeful pivot into pure commercial, civilian vendor (though subcontracting to defense industry still).
As for nuclear, civilian reactors aren't much of offshoot of bomb production except for using the same physical processes underneath.
Civilian nuclear reactors exist to keep 50-200kg of weapons grade plutonium on hand and ready to separate at all times. It's not shelf stable and a pure Pu manufacturing program is much harder to get social license for.
Majority of reactors in civilian use (outside some research ones) are really, really incapable of properly breeding plutonium, partially because of fears by "nuclear haves" that "have nots" would be able to produce weapons even if under NPT they have inspections etc. to notice that.
In fact, civilian nuclear reactors are just as much likely to consume plutonium in MOX fuels. All warhead manufacturing countries have separate, optimized production chains for plutonium.
Unless the fuel rods were highly enriched, below usable for reprocessing.
It's literally why USA had been more or less legally trying to stop everyone from running highly-enriched fuels in reactor (or generally make itself a nuisance for projects that in turn require no enrichment at all, because that stops dependency on limited enrichment facilities).
You're conflating two things and applying them to a third unrelated situation.
High enriched U is a proliferation risk because it's easier to enrich to weapons grade.
Fuel rods that have been through a full fuel cycle are 'useless' because of the Pu 240.
Fuel rods that have been in a reactor for 1-2 years (present in every 'civilian' reactor at all times) are neither of these things. And contain weapons grade Pu that can be used if you have Pu separation facilities.
Spacexs first dod contract was in 2016. Spacex successfully landed their first falcon in 2015. They were already the company we know and 'love' prior to them getting any dod contracts.
While Falcon 1 was developed on internal funding, the first two launches were paid for by DoD through DARPA. There was also a 15 million USD contract to launch a military satellite in 2005, that ultimately fell through (unknown how much was paid to SpaceX by the time of cancellation, but definitely not 0). In 2005, SpaceX boasted USAF as customer lined up for Falcon 1 launches.
Ultimately, first 2 launches the customer was purely military, and third launch by SpaceX was shared military / NASA / civilian client.
