$snick(#,0) returns the total number of selected users in the channel, not the names of the users.

It's not possible to select all the nicknames. You can only select one at a time through /sline.

However, you may return all the selected nicknames through the $snicks identifier.

Alternatively, you can use raws to retrieve all the nicknames in the channel like so:

Code:
on me:*:JOIN:#channel: { set $+(%,names.,$cid,.,#) }
raw 353:*: {
  if ($var($+(%,names.,$cid,.,$3))) {
    set $+(%,names.,$cid,.,$3) $($+(%,names.,$cid,.,$3),2) $right($4-,-1)
  }
}
raw 366:*: {
  if ($($+(%,names.,$cid,.,$2),2)) {
    msg $2 Hello, $v1
    unset $+(%,names.,$cid,.,$2)
  }
}

- Relinsquish