Can you charge a tablet and use a USB device at the same time?

I am not sure which question you are asking so I am going to answer the one that has an answer other than "It depends on the tablet in question"

You mention the Dell venue 8 Pro in your question. For that tablet Dell sells an adapter that does exactly what you want. It's called Dell MicroUSB Dongle For Data and Charging (470-ABES), "Dell Micro USB Dongle for Data and Charging" should bring it up on google.

You can also go the cheaper route and buy several cables and make your own. I don't see it as really worth the savings especially seeing the way too high gauge of wire common in cheap USB cables which cuts down charging speed significantly. How to use USB devices with your Dell Venue 8 Pro and charge it at the same time on Todd Klindt's SharePoint Admin Blog goes into this in greater detail but what it boils down to is when a cable is first plugged in the Venue checks to see if the data pins are shorted. If they are it allows it to charge. If not then it treats it as data. The key is that it only checks once. If by some miracle the data wires come unshorted and hook themselves to a data device the Venue will happily talk to said data device. Or usb to DVI video card. Or whatever.