> Q: Is it possible to use a relative pronoun in ON: "Ek sé mann, er
> tekr ost/er ost tekr." Most likely "já", but it never hurst to ask.

It's a valid sentence.

Ek sé mann, er tekr ost.
I see a man that takes some cheese.

Kveðja,
Haukur

--
He played the king as if afraid someone else would play the ace.
-- John Mason Brown, drama critic