Were these files also OMF, or did they use a different file format?
Short answer: Nope, all the same (with some extensions over the years)
The long story.
Intel originally intended PL/I to be the main language for 8008 and 8080 systems and made their PL/M compiler able to produce absolute code as well as relocatable one.
There where variations for each CPU, including the 8080, but the basic format was all the same.
The original Digital Research ASM did create Intel hex files, marked
.HEX. Similar did their Macro Assembler MAC.
Digital's Relocating Macro Assembler (RMAC) later added the optional ability to produce relocatable output (
.REL) as described in the LINK-80 manual
Microsoft's M80 turned assembly output by default into relocatable format as it was meant to work in cooperation with other high level languages from Microsoft which only created relocatable formats.
Microsoft as well as Digital Research used Intel's format for their relocatable formats. After all, it makes sense to be compatible as newcomer, doesn't it?
Intel called their files already
.OBJ, DR decided on
.REL while MS stuck with
.OBJ. They are all Intel OMF with the same basic logic and encoding format for all (ofc, MS added a lot over the years - already starting with M80). In theory, even the latest (separate) MS linker should be able to decode all records and produce 8080
.COM files. In theory at least :))
P.S.: The history then continued with Microsoft switching for (their version of) COFF - which by MASM 8.0 (ca.2005) even became default format.