I wouldn't call it "related" or even "similar"… it's similar in that they're both key value stores, but there's no durability and Ramcloud stores both keys & values in memory; whereas bitcask only stores keys in memory as an "index" to the value on disk.

Your operating includes a page cache (in some cases it may have even more e.g., ZFS on Solaris with ARC). It can very effectively load these indexed values into memory. Of course your own cache and direct I/O may be more efficient if you're building a search index or a relational database, but for a key/value store the page cache should be very effective.