I have noticed this in Julia 1.10 and 1.11.

I agree, a strange usage but I tripped over it in a real-world use case.

julia> 0x01+0x01im
ERROR: ParseError:    
# Error @ REPL[1]:1:6
0x01+0x01im           
#    └────┘ ── invalid numeric constant

The same goes for other bases and sizes.
This works fine, though:

julia> 0x01+0x01*im
0x01 + 0x01im