Yes, he did.
This was a fairly common thing for him to do; many of his stories demonstrate this behavior. It's more true with his Juvenile works, but it was common for him to specifically write his characters so that the reader would identify with them, not indicating anything about race, only later to drop some kind of information that hinted pretty strongly as to what that race was. By this point, having identified with the character, the reader is more prone to identify with his/her race somewhat. (Even where he didn't do this, it's surprising how often his main character is of indeterminate / not-pointed-out race; people reading will tend to assume that s/he is of their own race, regardless of what that race is.)
Some other examples:
- Juan Rico was Filipino, as you mentioned.
- Rod Walker (Tunnel in the Sky) was Black. (Never directly mentioned, but hinted at very strongly and later confirmed in a letter.)
- Colin Campbell's race is never clearly identified, but late in The Cat Who Walks Through Walls, talking to a man described as 'as beautiful as a black panther' (and, incidentally, given the nickname 'Sambo') he says "Look, boy, I'm mighty glad that your skin color matches mine." "Why so?" "Because, if it didn't, I would be called a racist for the way I despise you."
- Eunice (I Will Fear No Evil) never has her race identified, and, reportedly, RAH wrote that novel with two pictures of women used as inspiration, one Black, one White, just to keep himself from accidentally falling into describing her as a specific race.
It was less because he was just trying to mentally jerk people around, and more because he felt the race issue to be an irrelevant short-term issue of biology, that people made a huge deal out of; Genetically speaking 'racial purity' was nonsense; people paid too much attention to external indicators. †
In Friday, the title character (always portrayed as a pretty white woman on covers) is told about her genetic makeup and that 'You can never afford to be racist; you would bite your own tail!'
But far more telling (re: long term significance) is the passage from Time Enough for Love:
"Not that slant of eye or color of skin matters today, or even matters at the moment of truth. One of the early Howards was Robert C. M. Lee, of Richmond, Virginia-anybody know what his name was originally?"
"I do," I answered.
"Of course you do, Justin, so keep quiet-and that includes you, Athene. Anyone else?"
No one answered; Lazarus went on: "His birth name was Lee Choy Moo; he was born in Singapore, and his parents came from Canton in China-and of the people in the 'New Frontiers' he was a mathematician second only to Andy Libby."
"Goodness!" said Hamadryad. "I'm descended from him- but I didn't know he was a great mathematician."
"Did you know he was Chinese?'
"Lazarus, I'm not sure what 'Chinese' means; I haven't studied much terrestrial history. Isn't it a religion? Like 'Jewish'?"
"Not exactly, dear. The point is that it no longer matters. Just as few know and no one cares that the famous Zaccur Barstow, my partner in crime, was a quarter Negro. Does that word mean anything to you, Hamadarling? Not a religion."
"The word means 'black,' so I assume that one of his grandparents was from Africa."
"Which shows what comes of assuming anything on one datum. Two of Zack's grandparents, both mulatto, came from Los Angeles in my homeland. Since my line mixed with his a long time back, probably any of you can claim African ancestry. Which is statistically equivalent to claiming descent from Charlemagne.
† Before someone brings up Sixth Column, you should be aware that his story was predicated on a new (1941) theory involving how blood types fell into radical groups, that, among other things, were grouped along racial lines. This later proved to be false, but he was working with what was believed to be current science, not just a racist concept that he invented.