UA couldn't stop you entering the SQ Krisflyer Gold lounges because they have *G designation, but - assuming the one in T2 is the same as T3 - it is inconceivable that the SATS lounges could be any worse.
In fact, if the SATS lounges contain just a single toilet (restroom, bathroom) that would put them several light years ahead of what SQ provide, which is nothing short of disgraceful in their main airport ...