The question is concerned about by almost all FFXIV Gil buyers. It can not be answered simply "yes" or "no", because SE did ban some accounts with large amounts of Gil on Sep. 28, 2013. The ban case has caused a wide range of discussion and got SE into much trouble. However, since then, SE never ban FFXIV Gil buyers in the past three months, in the meantime, SE is irregularly keeping ban of GIL farmers.
Currency is more important in FFXIV than in any other MMORPG. As you know, there is almost no GIL drop, and it is worthless if you sell materials and gears to vendors. Therefore, as an enterprising adventurer, it is necessary to buy Gil if you do not have time to farm materials by yourself. Actually, it is the same as any other MMORPG.
I have been playing games since 2000 and selling game currency since 2004, never heard players’ accounts got banned because they bought currency. For example, if Blizzard bans gold buyers, most of the players already got banned, for there are millions of players have been bought gold, in this case the game WOW should have died already. For SE’s another game FFXI, a player who talked about this ban case said that " I knew a number of people who bought gil in ffxi and never even received a warning about it unless they talked about it openly/bought very large quantities."
Hundreds and thousands of FFXIV players have bought FFXIV Gil from our site Mmogah.com since the first release of Final Fantasy XIV in 2010, never heard any one of them got banned because they bought FFXIV Gil from us. Furthermore, millions of players have bought FFXIV Gil from innumerable other sites and players. If SE bans all of them, you can guess what will happen. So, I think the reason why SE banned some accounts with a large number of Gil before is because SE made a false judgement that they thought mistakenly those accounts as farmers.
As stated above, in my opinion, FFXIV Gil buyers won’t get banned. Before you buy FFIXV Gil, the things you should concern about are to avoid buying Gil from scammers(players or sites), and if the seller has instant delivery.