Several compilers come with their own VGA graphics libraries. A 3rd party developer has even developed an SVGA library (with drivers) for emx/gcc.
Full-screen graphics programming is nearly identical to full-screen DOS graphics programming, with the notable exception that you must lock and unlock the screen under OS/2 before you can use it.
For fast direct-access screen graphics, check at ftp-os2.cdrom.com, the file dlib06.zip.