Work-permit limbo looked set to leave Bruce without his club's record signing, before the Uruguay international striker had a solitary Sunday training session with his new team-mates.
Hernandez did enough to be included from the start at the KC Stadium and powered home a superb 39th-minute header to open the scoring before West Ham twice battled back to claim a pulsating 2-2 draw in the Premier League.
And Bruce was pleased to see the 24-year-old replicate the promise his solitary training stint with an all-action display.
"It was just his attitude," Bruce said. "He's been back [from international duty] and in Europe for three, four, five [days] waiting patiently for his passport.
"So we went to Croydon to the office for it, we flew to Rome with it and met him there in Rome.
"He only got here on Saturday afternoon, Sunday he was training and he was desperate to play. I'm so pleased we did it, even though he can hardly move now, but he'll be fine."
West Ham's Ecuadorian debutant Enner Valencia sparked a memorable second half with a scintillating 25-yard strike to haul Sam Allardyce's men level after 50 minutes.
Mohamed Diame, making his bow in midfield for Hull after joining from West Ham on deadline day, threatened to leave his former employers red-faced when he capitalised on slack defending to restore the home team's advantage.
But another striker making a maiden start, Diafra Sakho, drilled an angled effort that went in off Hull captain Curtis Davies to ensure a share of the spoils.
Bruce and Allardyce are noted for producing defensively robust teams that are hard to beat and the former allowed himself a wry smile after the duo set up contest enhanced by attacking formations and South American flair.
"I'm just going to go and have a beer with Sam... we're not really supposed to be playing like this, Sam and myself," he quipped.
'Sam and I both playing diamonds? Usually we're just buying diamonds for people's fingers.
"It was a really entertaining game of football. When I analyse it later I'll probably think it was a point gained.
"We've both brought people in to add fire power and score goals but there's also a knack of keeping people out which we need to do too."
