To summarize, as separate tickets UA will not interline bags for this case as it does not meet the MCT for DI UA-SQ at EWR. Additionally, there would not be the time to pick up bags and recheck. It would be a tight, high risk connection for a no check bag situation.
Results from
https://www.ExpertFlyer.com
Minimum Connect Times:
Connecting at EWR
Incoming airline UA
Outgoing airline SQ
Flight type Domestic to International
STANDARD.D/D...D/I...I/D...I/I.
ONLINE 1.00 1.15 1.30 1.00
OFFLINE 1.00 1.15 1.30 1.00
** OR * ARE ALL
UA-** DI 2.00