7-segment blue LED display at 3.3V
A reasonable guess would be that you'll be fine if the LEDs appear bright enough to you. 

4000-series CMOS is capable of very little current with a 3.3V supply, so the output transistors are acting like current sources/sinks. Typical is only 1mA at 5V supply. 

Of course if you're using 74HC4000 series rather than the datasheet you linked, the situation would be a bit different.