Yes, it's definitely possible to have one-way relationships in both directions simultaneously, and to have one-way relationships with some people and two-way with others in the same domain. For example, although she's not on my flist (nor, obviously, vice versa) I have seen Elizabeth Bear's comments on certain journals on my flist, so she's interacting with some and broadcasting to others.

And of course simply having the relationship available doesn't mean it's actually there; I endeavor to comment on flist posts which interest me, and thus build a relationship, but often people read each others' posts and never comment, and so I don't think they fall into each others' "Dunbar circles", so to speak - they don't take up space in each others' mental network, or perhaps they take up less space than, say, someone they regularly comment to and receive comments from.