In San Juan, casual is the acceptable dress for all the casinos I visited while there pre-cruise a year ago. In three day, went to all the casinos with shorts and had no problem. There are some unusual rules however. At El Casino in Old San Juan, you could not play at the tables with a hat or cap on your head. And, only one hand on cards in three card poker. So, better practice putting your cards under your bet with one hand.
At the Ritz-Carlton, there is a dress code. Seems like we had to undergo a credit check to get a player's card. Table limits started at $25 and $50. There were no $1 chips on the table that I could see, but went to the crap table where I sucessully talked the stickman out of 25 $1 chips, gave him a tip and left.
If my memory is correct in San Marteen, the only table games we saw were on the Duth side of the island.
Hope this help. Good luck.