Vuckic and Hiwula, on loan from Newcastle United and Huddersfield Town respectively, have been given the green light to feature for City in the FA Cup in this season's competition.
Fellow loanees Josh Cullen and Marc McNulty won't feature in the Accrington match, however, after being denied permission to play by their parent clubs.
McCall said: "It is 50% for us in terms of the four loan players.
"West Ham won't let Josh play and Sheffield United won't allow Marc to play.
"On the flip side though, Jordy Hiwula and Haris Vuckic can play.
"Two out of the four, we'll settle for that."
The absence of Cullen at the weekend means City will be forced into making at least one change from last Saturday's starting line up at AFC Wimbledon.
With competition for places currently as strong as ever within the City camp though, McCall is likely to use the Accrington fixture as an opportunity freshen things up and give some of his squad members a chance to impress.
Tony McMahon will be hoping to use this Saturday's cup tie as his comeback match following recent injury but the right back is currently a doubt after suffering a minor set-back on the training ground.
James Meredith is back in training after missing the last three games with an ankle problem, with the Australian set to be assessed pre-match to see if he could feature against Stanley.
McCall added: "We had to pull Tony back slightly.
"He is pushing so hard to be involved as quick as possible but he suffered a very slight reaction recently, nothing major.
"He'll be a doubt for Saturday but I'm sure he'll be back to full training by Monday.
"With James, he has trained and worked with the physio and fitness coach this week.
"He trained with us today (Thursday) and now, injury-wise, he is fine.
"Whether he is actually fit enough to start on Saturday after missing the last few games is something we will need to discuss.
"He is free of his injury now but we will need to speak with our fitness/physio department and James himself to see if he is ready to be put back in Saturday."