Depends on how good the tiler was!
Depends how thick the tiles are, 1/4" ceramic isn't as strong as 1" quarry.
Also depends how good the concrete sub base is.
Use a board to spread the load if you are uneasy, I'm assuming it's a regular stand, normally with 5-6 feet on the bottom. Each of these has the ability to pop through a tile if there is any void within the adhesive, which is probably likely as the adhesive tool (floor adhesive float/trowel) has notches to rib up the adhesive, these are an inch wide up to 3/4 deep with a half inch space between. If the sub floor was in a near perfect condition maybe a wall type adhesive trowel was used in which case there would be fewer and smaller voids.
When I installed a tank on an upper floor level I put the stand on an old section of kitchen worktop to ensure the load was spread. 1/2" or 3/4" Plywood would've worked but worktop was on hand.
(You could knock out the offending tiles and pour in a screed, depends on what is acceptable, if the floor is out of level then that's possibly a good route)
My first fish room was quarry tiles on concrete with a self levelling screed.
I was reiterating ppo's point because I entirely agreed. You're right in that I probably could have shut up and just +1 ' d it... I'll see myself out... 
