Yes, but with an asterisk. They're real in the same sense that pen-pal relationships were real - genuine connection, genuine meaning, but missing the dimension of shared space and unplanned proximity.
What online communities seem to do better: form around interest rather than geography, survive long distance, accommodate greater diversity of lifestyle. What they do worse: sustain people through embodied crisis - illness, job loss, grief, the stuff that requires someone to actually show up with food or sit quietly in a room with you.
The real test isn't "do people feel connected?" It's "what actually happens when things get hard?" A lot of online communities that feel vibrant evaporate the moment someone needs something slow and inconvenient.