I can expand a bit on how advantage play can work for the hold'em games against the house. I'm sure Grosjean and other professionals at this sort of thing have more sophisticated tactics. Fun fact - last I looked maybe 6-7 years ago, his book was selling for low 4 figures on the secondary market. That's how much advantage players can value an unknown tactic.

About 10 years ago casinos started offering various hold'em variants played against the house, presumably to cash in on the poker boom that was going on. Most of them try to mimic the flow of a hold'em hand as much as possible. You'll always have to ante something (somewhat analogous to posting a blind, but also just required as a way to force action in a table game), and then generally there's a decision point after getting your hole cards where you can bet more or fold. The more complicated games include additional decision points after seeing the flop and sometimes the turn. There's a lot more details I'm glossing over here about how it works (dealer hand must qualify by being a minimum strength, different payouts for various final hand strengths, different allowable bet sizes, bonus bets, etc.), but that's the basic structure. I recall seeing 3 major variants at the time - from least complicated to most, WPT All-in Hold'em, Texas Hold'em Bonus (I think, whatever the WSOP branded one was that Harrah's had), and Ultimate Texas Hold'em. WPT seems dead, UTH I still see around a bit. Not sure if Harrah's and other places still run Bonus.

The basic strategy for all these games generally involves a simple lookup table for the preflop action - for WPT, the correct play is to max bet for 90+% of your hands [1]- it's a very easy game to play perfectly. For UTH, it's probably closer to 25% [2]. (Aside - ignoring bankroll considerations, it's almost always correct to bet the max on any game that allows a range of bets. Either the bet is +EV or it isn't.)

The easiest advantage you can take is to simply know more cards at the table. Most dealers in my experience will allow you to show cards to your friends, ask for advice, whatever. Knowing more cards lets you make better decisions. Simple example - in WPT 83 offsuit is a very borderline playable hand. If you see another 8 in a player's hand, that may make it unplayable (since you're less likely to make a pair of 8s). Alternatively, if you have a borderline unplayable hand, seeing a pair of high cards in another hand may make the dealer less likely to qualify, which is an advantage for you when you have any bad hand.

In WPT at least, this is an extremely minor advantage - the "strategic frontier" where your decisions may be changed by this knowledge is extremely small. It's theoretically a much larger advantage in UTH, but there the strategy changes you can make with this knowledge encompass such a huge state space that you'll not be able to apply it consistently.

A second advantage is touched on in the article, viewing the dealer's hole cards. This is much harder to do and usually involves finding a dealer with bad form - I believe they're trained to slide the cards right out of the machine along the felt to avoid this, but some dealers lift slightly, so you can catch glimpses if you're in the right seat. Hopefully the playing advantages of knowing the dealer's cards are obvious.

I wouldn't be surprised if shuffle tracking is employed as well, but I'm not really sure what the state of the shuffle machines is these days.

Surprisingly, the biggest advantage I ever saw was to simply understand how to evaluate a hold'em hand. I've played hundreds of thousands of hands (former pro), and I still get it wrong occasionally when I'm not paying attention. When all these games first came out, casinos had to train dealers to do this, many of whom had never played poker. I think I calculated that I'd need to see a mistake rate of something like 1/600 to make the game profitable right out of the gate, ignoring any other advantages, and I was seeing 2-3 mistakes/hr (out of maybe 30-100 hands/hr). Admittedly only about half of the mistakes will be in your favor. It's not quite as easy these days, but for the first year or so it was an absolute gold mine.

Orthogonal to all this, some of these games are pretty easy to play at 98+%. Watching how people play these games, I wouldn't be surprised if the average table hold is upwards of 10%. I don't have any particular proof, but I'm pretty sure I've gotten grossly overcomped for play at these games.

[1] Everything but 82o, 73o-, 63o-, 52o, 43o, 32o. I'm not sure why 53o is playable.
[2] Something like Ax+, K5o+, K2s+, Q5s+, Q7o+, J8s+, JTo, 33+. You can find the full table at wizardofodds or similar sites.