is there an Arduino IDE equivalent for them?
not that I know of. There is a C compiler (SDCC) but it doesn't have a very good reputation. There are also commercial C compilers. But 8051s are most often programmed in assembler. (there is also 8052 BASIC, but I don't know if there is a version for these particular chips, and it usually needs external RAM.)
More to the point, how do I even hook them up? Do they need an external crystal?
Yes. Of somewhat unusual frequency, to get the serial bootloader to work.
Can I re-purpose and Arduino UNO board (without the arduino chip) to communicate with them?
yes, probably.
Try looking at http://www.8052.com/ for a start.
Also, PJRC (of Teensy fame) used to do 8051 stuff and still has some resources on their page.