redis is already apart of Cloudron
Yes & no,
Yes is part of the cloudron addon, but it can be integrated in different way.
You can use it for dynamic cache (as cloudron use in there apps), behind the php, db lvl.
You can use it as a Full Page Cache (similar to what Cache Enebler do but in RAM and not in local disc). php lvl
You can use it for partial page caching, in this case is at webserver/proxy lvl.
Redis is just a "database" in RAM, you can use it to store what you want, Redis is not a cache, but you can use it as it was one.