Yes this is well possible. But I haven't found any evidence for the name
SILAS being used as a short form of
SILVANUS in a Greek-Roman context. I'd be glad to read about that.
If this is true, the two names would look alike just by incidence. Same as
JUTTA in Germany: This is a
German form of
Judith and a Germanic name of its own right. The latter fact helped a lot to make the biblical name popular in Germany.
The biblical
SILAS was a Jew, so I'd rather explain his name from
SAUL.