If I reveal Guards, can I play the Sand Soldier to base?

No, you cannot play the Sand Soldier token created by Guards! to your base.

According to RiftJudge FAQ #8658, when you play a spell with the Hidden keyword (like Guards!) from its facedown position, any units it creates must be played at the same battlefield where the card was hidden.

This is further supported by Rule 737.1.d.3, which states: "If a hidden spell or a play effect of a hidden permanent causes you to play a unit, you must choose to play that unit at that battlefield [where the card was hidden]."

Because Guards! is a spell that creates a unit token, the token must enter play at the battlefield where the Guards! card was hidden. It cannot be played to your base.