There was a function called UTIL_Setspark or something. Look where this function is defined i guess there is other functions about that blood spray above and below.
then check UTIL_setsparks definiton. i guess there is functions about TE_spark or something. Go where TE_spark defined. You'll see List of Temporary entities Starts with TE_ there should be blood entity or similar, use it for making your own function like UTIL_setspark. It shouldn't necasserily to be a blood entity any particle effect may be used to simulate original blood.
İf there isn't a temp entity about it, i believe this feature still exist in engine, but i dont know how to make dll functions to call this feature.
Email who made similar alpha half-life mods they may give you further information.
And you have to search these sites and these functions to learn.documentation(amxmodx.org)alliedmods.net(search something like "write_byte(TE_PLAYERDECAL)" to find how people use theese functions)